Chapter 2

PL. I

WEALDEN AND LOWER GREENSAND

Those were the days of reptiles. Now the earth is the domain of the mammalia. But then great reptiles like the Iguanodon wandered over the land; great marine reptiles, such as the Plesiosaurus, swam the waters; and wonderful flying reptiles, the Pterodactyls, flew the air. Some species of these were quite small, the size of a rook: one large species found in the Isle of Wight had a spread of wing of 16 feet. Imagine this strange world,—its forests with pines and monkey puzzles and cycads,—ferns also, of which many fragments are found,—its great reptiles and little reptiles, on land, in the water and the air. Were there no birds? Yes, but they were rare. From remains found in Oolitic strata,—somewhat older than the Wealden,—we know that birds were already in existence; and they were as strange as anything else. For they had jaws with teeth like the reptiles. They had not yet adopted the beak. And instead of all the tail feathers starting from one point, as in birds of the present day, these ancient birds had long curving tails like reptiles, with a pair of feathers on each joint. Birds of similar but slightly more modern type have been found in Cretaceous strata (to which the Wealden belongs) in America, but so far not in strata of this age in Britain.

Among other objects of interest along this Wealden shore may be noticed a curious transformation which has affected the surface of some of the shell limestones after they were formed, which is known as cone-in-cone structure. It has quite altered the outer layer of the rock, so that all trace of the shells of which it consists is obliterated. Numerous pieces of iron ore from various strata lie on the shore. Through most of English history the Weald of Kent and Sussex was the great iron-working district of England. The ore from the Wealden strata was smelted by the help of charcoal made from the woods that grew there, and gave the district its name;—forWealdmeans "forest." This industry gradually ceased, as the much larger supplies of iron ore found near the coal in the mines of the North of England came to be worked. Iron pyrites, sulphide of iron in crystalline form, was formerly collected on the Sandown shore, and sent to London for the manufacture of sulphuric acid. This mineral is often found encrusting fossil wood. It also occurs as rounded nodules (mostly derived from the Lower Chalk) with a brown outer coat, and often showing a beautiful radiated metallic structure, when broken. (This form is called marcasite.)

As we walk by the edge of the water, we shall see what pretty stones lie along the beach. When wet with the ripples many look like polished jewels. Some are agates, bright purple and orange in colour, some clear translucent chaldedony. We shall have more to say about these later on. They do not come from the Wealden, but from beds of flint gravel, and are washed along the shore. But there are also jaspers from the Wealden. These are opaque, generally red and yellow. There are also pieces of variegated quartz, and other beautiful pebbles of various mineral composition. These are stones from older rocks, which have been washed down the Wealden rivers, and buried in the Wealden strata, to be washed out again after hundreds of thousands of years, and rolled about on the shore on which we walk to-day.

[1]Blue clays of various geological age, which in wet weather become semi-liquid, and flow out on to the shore, are known in the Island by the local name ofBlue Slipper.

[2]The name now adopted isViviparus. There is also a band of ferruginous limestone mainly composed ofViviparus.

PL. II

LOWER AND UPPER GREENSAND

Chapter IV

THE LOWER GREENSAND

For ages the Wealden river flowed, and over its vast delta laid down its depth of river mud. The land was gradually sinking; for continually strata of river mud were laid down over the same area, all shallow-water strata, yet counting hundreds of feet in thickness in all. At last a change came. The land sank more rapidly, and in over the delta the sea water flowed. The sign of coming change is seen in the limestone band made up of small oysters near the top of the Wealden strata. Marine life was beginning to appear.

Above the Wealden shales in Sandown Bay may be seen a band of brown rock. It is in places much covered by slip, but big blocks lie about the shore, and it runs out to sea as a reef before we come to the Red Cliff. The blocks are seen to consist of a hard grey stone, but the weathered surfaces are soft and brown. They are full of fossils, all marine, sea shells and corals. The sea has washed in well over our Wealden delta, and with this bed the next formation, the Lower Greensand, begins. The bed is called the Perna bed, from a large bivalve shell (Perna mulleti) frequently to be found in it, though it is difficult to obtain perfect specimens showing the long hinge of the valve, which is a marked feature of the shell. Among other shells are a large round bivalveCorbis(Sphæra)corrugata, a flatter bivalveAstarte,—and a smaller oblong shellPanopæa,—also a peculiar shell of triangular form,Trigonia,—one speciesT. caudatahas raised ribs running across it, anotherT. dædaleahas bands of raised spots.A pretty little coral, looking like a collection of little stars,Holocystis elegans, one of the Astræidæ, is often very sharply weathered out.

Above the Perna bed lies a mass of blue clay, weathering brown, called the Atherfield clay, because it appears on a great scale at Atherfield on the south west of the Island. It is very like the clay of the Wealden shales, but is not divided into thin layers like shale.

Next we come to the fine mass of red sandstone which forms the vertical wall of Red Cliff. Not many fossils are to be found in these strata. Let us note the beauty of colouring of the Red Cliff—pink and green, rich orange and purple reds. And then let us pass to the other side of the anticline, and walk on the shore to Shanklin. Here we see the red sandstone rocks again, but now dipping to the south. You probably wonder why these red cliffs are called Greensand. But look at the rocks where they run out as ledges on the shore towards Shanklin. Here they are dark green. And this is really their natural colour. They are made of a mixture of sand and clay coloured dark green by a mineral called glauconite. Grains of glauconite can easily be seen in a handful of sand,—better with a magnifying glass. This mineral is a compound of iron, with silica and potash, and at the surface of the rock it is altered chemically, and oxide of iron is formed—the same thing as rust. And that colours all the face of the cliff red. The iron is also largely responsible for our finding so few fossils in these strata. By chemical changes, in which the iron takes part, the material of the shells is destroyed.[3]Near Little Stairs hollows in the rock may be seen, where large oyster shells have been. In some you may find a broken piece of shell, but the shells have been mostly destroyed. NearerShanklin we shall find large oysters,Exogyra sinuata, in the rock ledges exposed at low tide. Some are stuck together in masses. Evidently there was an oyster bank here. And here the shells have not been destroyed like those in the cliff.

From black bands in the cliff water full of iron oozes out, staining the cliff red and yellow and orange, and trickling down, stains the flint stones lying on the shore a bright orange. At the foot of the cliff you may sometimes see what looks like a bed of conglomerate,i.e., a bed of rounded pebbles cemented together. This does not belong to the cliff, but is made up of the flint pebbles on the shore, and the sand in which they lie, cemented into a solid mass by the iron in the water which has flowed from the cliff. It is a modern conglomerate, and shows us how old conglomerates were formed, which we often find in the various strata. The cement, however, in these is not always iron oxide. It may be siliceous or of other material. The iron-charged water is called chalybeate; springs at Shanklin and Niton at one time had some fame for their strengthening powers. The strata we have been examining are known as the Ferruginous sands,i.e., iron sands (Lat.ferrum, "iron"). Beyond Shanklin is a fine piece of cliff. Look up at it, but beware of going too close under it. The upper part consists of a fine yellow sand called the Sandrock. At the base of this are two bands of dark clay. These bands become filled with water, and flow out, causing the sandrock which rests on them to break away in large masses, and fall on to the beach.

It is clay bands such as these which are the cause of our Undercliffs in the Isle of Wight. Turn the point, and you see exactly how an undercliff is formed. You see a wide platform at the level of the clay, which has slipped out, and let down the sandrock which rested on it. Beyond Luccombe Chine a large landslip took place in 1910, a great mass of cliff breaking away, and leaving aravine behind partly filled with fallen pine trees. The whole fallen mass has since sunk lower and nearer to the sea. The broken ground overgrown with trees called the Landslip, as well as the whole extent of the ground from Ventnor and Niton, has been formed in a similar way. But the clay which by its slip has produced these is another clay called the Gault, higher up in the strata. At the top of the high cliff near Luccombe Chine a hard gritty stratum of rock called the Carstone is seen above the Sandrock, and above it lies the Gault clay, which flows over the edge of the cliff.

In the rock ledges and fallen blocks of stone between Shanklin and Luccombe many more fossils may be found than in the lower part of the Ferruginous sands. Besides bands of oysters, blocks of stone are to be found crowded with a pretty little shell calledRhynchonella. There are others with manyTerebratulæ, and others with fragments of sea urchins. The Terebratulæ and Rhynchonellæ belong to a curious group of shells, the Brachiopods, which are placed in a class distinct from the Mollusca proper. They were very common in the very ancient seas of the Cambrian period,—the period of the most ancient fossils yet found,—and some, the Lingulæ, have lived on almost unchanged to the present day. One of the two valves is larger than the other, and near the smaller end you will see a little round hole. Out of this hole, when the creature was alive, came a sort of neck, which attached it to the rock, like the barnacles. There is a very hard ferruginous band, of which nodules may be found along the shore, full of beautifully perfect impressions of fossils, though the fossils themselves are gone. Casts of a little round bivalve shell,Thetironia minor, may easily be got out. The nodules also contain casts of Trigonia, Panopœa, etc. A stratum is sometimes exposed on the shore containing fossils converted into pyrites. A long shell,Gervillia sublanceolata, is the most frequent.

All the shells we have found are of sea creatures, and show us that the Greensand was a marine formation. But the strata were formed in shallow water not far from the shore. We have learnt that coarse sediment like sand is not carried by the sea far from the coast. And a good deal of the Greensand is coarser than sand. There are numerous bands of small pebbles. The pebbles are of various kinds; some are clear transparent quartz, bits of rock-crystal more or less rounded by rolling on the shore of the Greensand period. These go by the name of Isle of Wight diamonds, and are very pretty when polished. Another mark of the nearness of the shore when these beds were laid down is the current bedding, of which a good example may be seen in the cliff at the north of Shanklin parade. It is sometimes called false bedding, for the sloping bands do not mark strata laid down horizontally at the bottom of the sea, but a current has laid down layers in a sloping way,—it may be just over the edge of a sandbank. Again notice how much wood is to be seen in the strata. Land was evidently not far off. All along the shore you may find hard pieces of mineralised wood, the rings of growth often showing clearly. Frequently marine worms have bored into them before they were locked up in the strata; the holes being generally filled afterwards with stone or pyrites.

The wood is mostly portions of trunks or branches of coniferous trees. We also find stems of cycads. There has been found at Luccombe a very remarkable fruit of a kind of cycad. We said that in the Wealden period none of our flowering plants grew. But these specimens found at Luccombe show that cycads at that time were developing into flowering plants. Wonderful specimens of what may almost be called cycad flowers have been found in strata of about this age in Wyoming in America; and this Luccombe cycad,—called Benettites Gibsonianus,—shows what these were like in fruit. Remains ofvarious cycadeous plants have been found in the corresponding strata at Atherfield; and possibly by further research fresh knowledge may be gained of an intensely interesting story,—the history of the development of flowering plants.

On the whole the vegetation of the period was much the same as in the Wealden. But these flowering cycads must have formed a marked addition to the landscape,—if indeed they did not already exist in the Wealden times. The cones of present day cycads are very splendidly coloured,—orange and crimson,—and it can hardly be doubted that the cycad flowers were of brilliant hues.

The land animals were still like the Wealden reptiles. Bones of large reptiles may at times be found on the shore at Shanklin. Several have been picked up recently. From the prevalence of cycads we may conclude that the climate of the Wealden and Lower Greensand was sub-tropical. The existing Cycadaceæ are plants of South Eastern Asia, and Australia, the Cape, and Central America. The forest of trees allied to pines and firs and cedars probably occupied the higher land. Turtles and the corals point to warm waters. The existing species of Trigonia are Australian shells. This beautiful shell is found plentifully in Sydney harbour. It possesses a peculiar interest, as the genus was supposed to be extinct, and was originally described from the fossil forms, and was afterwards found to be still living in Australia.

[3]Carbonate of lime has been replaced by carbonate of iron, and the latter converted into peroxide of iron. At Sandown oxidation has gone through the whole cliff.

Fig. 2

Coast Atherfield To Rocken EndCOAST ATHERFIELD TO ROCKEN ENDWlWealden Beds.WWalpen Clay.FerFerruginous Bands of Blackgang Chine.PPerna Bed.UcUpper Crioceras Beds.BBlack Clay.AAtherfield Clay.WSWalpen and Ladder Sands.SSandrock and Clays.CkCracker Group.UgUpper Gryphæa Beds.LgLower Gryphæa Beds.CeCliff End Sands.ScScaphite. "FFoliated Clay.LcLower Crioceras "SUSands of Walpen Undercliff.

Coast Atherfield To Rocken End

Chapter V

BROOK AND ATHERFIELD

To most Sandown Bay is by far the most accessible place in the Island to study the earlier strata; and for our first geological studies it has the advantage of showing a succession of strata so tilted that we can pass over one formation after another in the course of a short walk. But when we have learnt the nature of geological research, and how to read the record of the rocks, and examined the Wealden and Greensand strata in Sandown Bay, we shall do well, if possible, to make expeditions to Brook and Atherfield, to see the splendid succession of Wealden and Greensand strata shown in the cliffs of the south-west of the Island. It is a lonely stretch of coast, wild and storm-swept in winter. But this part of the Island is full of interest and charm to the lover of Nature and of the old-world villages and the old churches and manor houses which fit so well into their natural surroundings. The villages in general lie back under the shelter of the downs some distance from the shore; a coastguard station, a lonely farm house, or some fishermen's houses as at Brook, forming the only habitations of man we come to along many miles of shore. Brook Point is a spot of great interest to the geologist. Here we come upon Wealden strata somewhat older than any in Sandown Bay. The shore at the Point at low tide is seen to be strewn with the trunks of fossil trees. They are of good size, some 20 ft. in length, and from one to three feet in diameter. They are known as the Pine Raft, and evidently form a mass of timber floated down an ancient river, and strandednear the mouth, just as happens with great accumulations of timber which float down the Mississippi at the present day. The greater part of the wood has been replaced by stone, the bark remaining as a carbonaceous substance like coal, which, however, is quickly destroyed when exposed to the action of the waves. The fossil trees are mostly covered with seaweed. On the trunks may sometimes be found black shining scales of a fossil fish,Lepidotus Mantelli. (A stratum full of the scales ofLepidotushas been recently exposed in the Wealden of Sandown Bay.) The strata with the Pine Raft form the lowest visible part of the anticline. From Brook Point the Wealden strata dip in each direction, east and west. As the coast does not cut nearly so straight across the strata as in Sandown Bay, we see a much longer section of the beds. On either side of the Point are coloured marls, followed by blue shales, as at Sandown. To the westward, however, after the shales we suddenly come to variegated marls again, followed by a second set of shales. There was long a question whether this repetition is due to a fault, or whether local conditions have caused a variation in the type of the beds. The conclusion of the Geological Survey Memoir, 1889, rather favoured the latter view, on the ground of the great change which has taken place in the character of the beds in so short a distance, assuming them to be the same strata repeated. The conjecture of the existence of a fault has, however, been confirmed; for during the last years a most interesting section has been visible at the junction of the shales and marls, where a fault was suspected. The shales in the cliff and on the shore are contorted into the form of aZ. The section appears to have become visible about 1904 (it was in the spring of that year that I first saw it), and was described by Mr. R. W. Hooley, F.G.S. (Proc. Geol. Ass., vol. xix., 1906, pp. 264, 265). It has remained visible since.

The Wealden of Brook and the neighbouring coast is celebrated for the number of bones of great reptiles found here, from the early days of geological research, the '20's and '30's of last century, when admirable early geologists, such as Dr. Buckland and Dr. Mantell, were discovering the wonders of that ancient world, to the present time. Various reptiles have been found besides the Iguanodon—the Megalosaurus, a great reptile somewhat similar, but of lighter build, with sabre-shaped teeth, with serrated edges: the Hylæosaurus, a smaller creature with an armour of plates on the back, and a row of angular spines along the middle of the back; the hugeHoplosaurus hulkei, probably 70 or 80 feet in length; the marine Plesiosaurus and Ichthyosaurus, and several more; also bones of a freshwater turtle and four types of crocodiles. In various beds a large freshwater shell,Unio valdensis, occurs, and in the cliffs of Brook have been found many cones of Cycadean plants. In bands of white sandy clay are fragments of ferns,Lonchopteris Mantelli. In the shales are bands of limestone with Cyrena, Paludina, and small oysters, and paper shales with cyprids, as at Sandown. The shore near Atherfield Point is covered with fallen blocks of the limestones.

The Lower Greensand is seen in Compton Bay on the northern side of the Brook anticline. Here is a great slip of Atherfield clay. The beds above the clay are much thinner than at Atherfield, and fossils are comparatively scarce. On the south of the anticline the Perna bed slopes down to the sea about 150 yards east of Atherfield Point, and runs out to sea as a reef. Large blocks lie on the shore, where numerous fossils may be found on the weathered surfaces. The ledges which here run out to sea form a dangerous reef, on which many vessels have struck. There is now a bell buoy on the reef. On the headland is a coastguard station, and till lately there has been a sloping wooden way from the top of thecliff to bring the lifeboat down. This was washed away in the storms of the winter 1912-13.

Above the Perna bed lies a great thickness of Atherfield clay. Above this lies what is called the Lower Lobster bed, a brown clay and sand, in which are numerous nodules containing the small lobsterMeyeria vectensis,—known as Atherfield lobsters. Many beautiful specimens have been obtained.

We next come to a great thickness of the Ferruginous Sands, some 500 feet. The Lower Greensand of Atherfield was exhaustively studied in the earlier days of geology by Dr. Fitton, in the years 1824-47, and the different strata are still referred to according to his divisions. The lowest bed is the Crackers group about 60 ft. thick. In the lower part are two layers of hard calcareous boulder-shaped concretions, some a few feet long. The lower abound in fossils, and though hard when falling from the cliffs are broken up by winter frosts, showing the fossils they contain beautifully preserved in the softer sandy cores of the concretions.Gervillia sublanceolatais very frequent, alsoThetironia minor, the AmmoniteHoplites deshayesi, and many more. Beneath and between the nodular masses caverns are formed, the resounding of the waves in which has given the name of the "Crackers." In the upper part of this group is a second lobster bed.

The most remarkable fossils in the Lower Greensand are the various genera and species of the ammonites and their kindred. The Ammonite, through many formations, was one of the largest, and often most beautiful shells. There were also quite small species. The number of species was very great. Now the whole group is extinct. They most resembled the Pearly Nautilus, which still lives. In both the shell is spiral, and consists of several chambers, the animal living in the outer chamber, the rest being air-chambers enabling it to float. The class Cephalopoda, which includes the Ammonites, the Nautilus, and also theCuttle-fish, is the highest division of the Mollusca. The animals all possess heads with eyes, and tentacles around the mouth. They nearly all possess a shell, either external, as in the Nautilus, or internal, as in the cuttle-fishes, the internal shell of which is often washed ashore after a rough sea. The Cephalopods are divided into two orders. The first includes the Cuttle-fish and the Argonaut or Paper Nautilus. Their tentacles are armed with suckers, and they have highly-developed eyes. They secrete an inky fluid, which forms sepia. The internal shell of extinct species of cuttle-fish, of a cylindrical shape, with a pointed end, is a common fossil in various strata, and is known as a Belemnite (Gr.βελεμων"a dart".) The second order includes the Pearly Nautilus of the present day, and the numerous extinct Nautiloids and Ammonoids. The tentacles of the Pearly Nautilus have no suckers; and the eyes are of a curiously primitive structure,—what may be called a pin-hole camera, with no lens. The shells of the Nautilus and its allies are of simpler form, while the Ammonites are characterised by the complicated margins of the partition walls or septa, by which the shells are sub-divided. The chambers of the fossil Ammonites have often been filled with crystals of rich colours; and a polished section showing the chambers is then a most beautiful object.[4]

Continuing along the shore, we come to the Lower Exogyra group, whereTerebratula sellais found in great abundance. A reef withExogyra sinuataruns out about 350 yards west of Whale Chine. The group is 33 ft. thick, and is followed by the Scaphites group, 50 ft. The beds containExogyra sinuata, and a reef with clusters of Serpulæ runs out from the cliff. In the middle of the group are bands of nodules containingMacroscaphites gigas. The Lower Crioceras bed (16 ft.) follows, andcrosses the bottom of Whale Chine. The Scaphites and Crioceras are Cephalopoda, related to the Ammonites; but in this Lower Cretaceous period a remarkable development took place; many of the shells began to take curious forms, to unwind as it were. Crioceras, a very beautiful shell, has the form of an Ammonite, but the whorls are not in contact; thus making an open spiral like a ram's horn, whence its name (Gk.κέρος, ram,κριός, horn). Ancyloceras begins like Crioceras, but from the last whorl continues for some length in a straight course, then bends back again; Macroscaphites is similar, but the whorls of the spiral part are in contact. In Scaphites, a much smaller shell, the uncoiled part is much shorter, and its outline more rounded. It is named from its resemblance to a boat (Gk.σκάφη).[5]

The Walpen and Ladder Clays and Sands (about 60 ft.) contain nodules with Exogyra and the AmmoniteDouvilleiceras martini. The dark-green clays of the lower part form an undercliff, on to which Ladder Chine opens. The Upper Crioceras Group (46 ft.), like the Lower, contains bands of Crioceras? alsoDouvilleiceras martini, Gervillia, Trigonia, etc. It must be stated that there is some uncertainty with regard to the ammonoids found in this neighbourhood, Macroscaphites having been described as Ancyloceras, and also sometimes as Crioceras. The discovery of the true Ancyloceras (Ancyloceras Matheronianum) at Atherfield is described (and a figure given) by Dr. Mantell; but what is the characteristic ammonoid of the "Crioceras" beds requires further investigation. The neighbourhood of Whale and Walpen Chines is of great interest. Ammonites may be found in the bottom of Whale Chine fallen out of the rock. Red ferruginous nodules with Ammonites lie on the shore, in the Chines, and on the Undercliff, some of the ammonites more or less converted into crystalline spar.Hard ledges of the Crioceras beds run into the sea. The shore is usually covered deep with sand and small shingle; but there are times when the sea has washed the ledges clear; and it is then that the shore should be examined.

The Walpen and Ladder Sands (42 ft.); the Upper Exogyra Group (16 ft.); the Cliff End Sand (28 ft.); and the Foliated Clay and Sand (25 ft.), consisting of thin alternations of greenish sand and dark-blue clay, follow. Then the Sands of Walpen Undercliff (about 100 ft.); over which lie the Ferruginous Bands of Blackgang Chine (20 ft.). Over these hard beds the cascade of the Chine falls. Cycads and other vegetable remains are found in this neighbourhood. Throughout the Atherfield Greensand fragments of the fernLonchopteris(Weichselia)Mantelliare found. 220 ft. of dark clays and soft white or yellow sandrock complete the Lower Greensand. In the upper beds of the Greensand few organic remains occur. A beautiful section of Sandrock with the junction of the Carstone is to be seen inland at Rock above Bright-stone. The Sandrock here is brightly coloured like the sands of Alum Bay,—though it belongs to a much older formation,—and shows current bedding very beautifully. The junction of the Sandrock and Carstone is also well seen in the sandpit at Marvel.

We have now come to the end of the Lower Cretaceous, in which are included the Wealden and the Lower Greensand. Judged by the character of the flora and fauna, the two form one period, the main difference being the effect of the recession of the shore line, due to the subsidence which let in the sea over the Wealden delta, so that we have marine strata in place of freshwater deposits. But that the plants and animals of the Wealden age still lived in the not distant continent is shown by the remains borne down from the land. These strata are an example of a phenomenon often met with in geology,—that of a great thickness of deposits all laid down in shallow water.The Wealden of the Isle of Wight are some 700 feet thick, in Kent a good deal thicker, the Hastings Sands, the lower part of the formation, being below the horizon occurring in the Island: the Lower Greensand is some 800 feet thick. In the ancient rocks of Wales, the Cambrian and Silurian strata, are thousands of feet of deposits, mostly laid down in fairly shallow water. In such cases there has been a long-continued deposition of sediment, while a subsidence of the area in which it was laid down has almost exactly kept pace with the deposit. It is difficult not to conclude that the subsidence has been caused by the weight of the accumulating deposit,—continuing until some world-movement of the contracting globe has produced a compensating elevation of the area.

[4]Some fine ammonites may be seen at the Clarendon Hotel, Chale,—one about 5 ft. in circumference.

[5]See Guide to Fossil Invertebrata, Brit. Mus. Nat. Hist.

Chapter VI

THE GAULT AND UPPER GREENSAND

We have seen how the continent through which the great Wealden river flowed began to sink below the sea level, and how the waters of the sea flowed over what had been the delta of the river, laying down the beds of sandstone with some mixture of clay which we call the Lower Greensand. The next stratum we come to is a bed of dark blue clay more or less sandy, called the Gault. In the upper beds it becomes more sandy and grey in colour. These are known as the "passage beds," passing into the Upper Greensand. The thickness of the Gault clay proper varies from some 95 to 103 feet. Compared to the mainland the Gault is of small thickness in the Island, though the dark clay bands in the Sandrock mark the oncoming of similar conditions. The fine sediment forming the clay points to a further sinking of the sea bed. In general, we find very few fossils in the Gault in the Island, though it is very fossiliferous on the mainland at Folkestone. North of Sandown Red Cliff the Gault forms a gully, down which a footpath leads to the shore. It is seen at the west of the Island in Compton Bay, where in the lower part some fossil shells may be found.

The Upper Greensand is not very well named, as the beds only partially consist of sandstone, in great part of quite other materials. Some prefer to call the Lower Greensand Vectian, from Vectis, the old name of the Isle of Wight, and the Upper Greensand Selbornian, a name generally adopted, because it forms a marked feature ofthe country about Selborne in Hampshire.[6]But, though the Upper Greensand covers a less area in the Isle of Wight than the Lower, it forms some of the most characteristic scenery of the Island. One of the most striking features of the Island is the Undercliff, the undulating wooded country from Bonchurch to Niton, above the sea cliff, but under a second cliff, a vertical wall which shelters it to the North. This wall of cliff consists of Upper Greensand. In a similar way to the small undercliffs we saw at Luccombe, the Undercliff has been formed by a series of great slips, caused here by the flowing out of the Gault clay, which runs in a nearly horizontal band through the base of all the Southern Downs of the Island, the Upper Greensand lying above it breaking off in masses, and leaving vertical walls of cliff. These walls are seen not only in the Undercliff, but also on the northern side of the downs, where they form the inland cliff overhanging a pretty belt of woodland from Shanklin to Cook's Castle, and again forming Gat Cliff above Appuldurcombe. We have records of great landslips at the two ends of the Undercliff, near Bonchurch and at Rocken End, about a century ago. But the greater part of the Undercliff was formed by landslips in very ancient times, before recorded history in this Island began. The outcrop of the Gault is marked by a line of springs on all sides of the Southern Downs. The strata above, Chalk and Upper Greensand, are porous and absorb the rainfall, which permeates through till it reaches the Gault Clay, which throws it out of the hill side in springs, some of which furnish a water supply for the surrounding towns and villages.

Where the Upper Greensand is best developed, above the Undercliff, the passage beds are followed by 30 feet of yellow micaceous sands, with layers of nodules of a bluish-grey siliceous limestone known as Rag. The nodules frequently contain large Ammonites and other fossils. Next follow the Sandstone and Rag beds, about 50 feet of sandstone with alternating layers of rag. The sandstones are grey in colour, weathering buff or reddish-brown, tinged more or less green by grains of glauconite. Near the top of these strata is the Freestone bed, a thick bed of a close-grained sandstone, weathering a yellowish grey, which forms a good building stone. Most of the churches and old manor and farm houses in the southern half of the Island are built of this stone. Then forming the top of the series are 24 feet of chert beds,—bands of a hard flinty rock called chert alternating with siliceous sandstone, the sandstone containing large concretions of rag in the same line of bedding. The chert beds are very hard, and where the strata are horizontal, as above the Undercliff, project like a cornice at the top of the cliff. Perhaps the finest piece of the Upper Greensand is Gore Cliff above Niton lighthouse, a great vertical wall with the cornice of dark chert strata overhanging at the top. The thickness in the Undercliff, including the Passage Beds, is from 130 to 160 ft.

The Upper Greensand may be studied at Compton Bay, and at the Culvers; and along the shore west of Ventnor the lower cliff by the sea consists largely of masses of fallen Upper Greensand, many of which show the chert strata well. In numerous walls in the south of the Island may be seen stone from the various strata—sandstone, blue limestone or rag, and also the chert.

Let us think what was happening when these beds were being formed. The sandstone is much finer than that of the Lower Greensand; and we have limestones now,—marine, not freshwater as in the Wealden. Marine limestones are formed by remains of sea creatures living at some depth in clear water. And now we come to a new material, chert. It is not unlike flint, and flint is one of the mineral forms of silica. Chert may be called animpure or sandy flint. The bands of chert appear to have been formed by an infiltration of silica into a sandstone, forming a dense flinty rock, which, however, has a dull appearance from the admixture of sand, instead of being a black semi-transparent substance like flint. But where did the silica come from? In the depths of the sea many sea creatures have skeletons and shells formed of silica or flint, instead of carbonate of lime, which is the material of ordinary shells and of corals. Many sponges, instead of the horny skeleton we use in the washing sponge, have a skeleton formed of a network of needles of silica, often of beautiful forms. Some marine animalcules, the Radiolaria, have skeletons of silica. And minute plants, the Diatoms, have coverings of silica, which remain like a little transparent box, when the tiny plant is dead. Now, much of the chert is full of needles, or spicules, as they are called, of sponges, and this points to the source from which some at least of the silica was derived. To form the chert much of the silica has been in some manner dissolved, and deposited again in the interstices of sandstone strata. We shall have more to say of this process when we come to speak of the origin of the flints in the chalk. Sponges usually live in clear water of some depth; so all shows that the sea was becoming deeper when these strata were being formed.

Along the shore of the Undercliff, Upper Greensand fossils may be found nicely weathered out. Very common is a small curved bivalve shell,—a kind of small oyster,—Exogyra conica, as are also serpulæ, the tubes formed by certain marine worms. Very pretty pectens (scallop shells) are found in the sandstone. Many other shells,Terebratulæ,Trigonia,Panopæa, etc., occur, and several species of ammonite and nautilus.[7]A frequent fossil is a kind of sponge, Siphonia. It has the form of an oblong bulb, supported by a long stem, with a root-like base. It is often silicified, and when broken shows bundles of tubular channels.

In the chert may often be seen pieces of white or bluish chalcedony, generally in thin plates filling cracks in the chert. This is a very pure and hard form of silica, beautifully clear and translucent. Pebbles which the waves have worn in the direction of the plate are very pretty when polished, and go by the name of sand agates. They may sometimes be picked up on the shore near the Culvers.

[6]Names proposed by the late A. J. Jukes-Browne.

[7]Of Ammonites,Mortoniceras rostratumandHoplites splendensmay be mentioned: and of Pectens,Neithea quinquecostataandquadricostata,Syncyclonema orbicularis, andÆquipecten asper.

Chapter VII

THE CHALK

As we have traced the world's history written in the rocks we have seen an old continent gradually submerged, a deepening sea flowing over this part of the earth's surface. Now we shall find evidence of the deepening of the sea to something like an ocean depth. We are coming to the great period of the Chalk, the time when the material was made which forms the undulating downs of the south east of England, and of which the line of white cliffs consists, which with sundry breaks half encircles our shores, from Flamborough Head in Yorkshire, by Dover and the Isle of Wight, to Bere in Devon. Across the Channel white cliffs of chalk face those of England, and the chalk stretches inland into the Continent. Its extent was formerly greater still. Fragments of chalk and flint are preserved in Mull under basalt, an old lava flow, and flints from the chalk are found in more recent deposits (Boulder Clay) on the East of Scotland, pointing to a former great extension northward, which has been nearly all removed by denudation. In the Isle of Wight the chalk cliffs of Freshwater and the Culvers are the grandest features of the Island; while all the Island is dominated by the long lines of chalk downs running through it from east to west. Now what is the chalk? And how was it made? The microscope must tell us. It is found that this great mass of chalk is made up principally of tiny microscopic shells called Foraminifera, whole and in crushed fragments. There are plenty of foraminifera in the seas to-day; and we need not go far to find similar shells.On the shore near Shanklin you will often see streaks of what look like tiny bits of broken shell washed into depressions in the sand. These, however, often consist almost entirely of complete microscopic shells, some of them of great beauty. The creature that lives in one of these shells is only like a drop of formless jelly, and yet around itself it forms a complex shell of surprising beauty. The shells are pierced with a number of holes, hence their name (fr. Lat.foramen, a hole, andferre, to bear). Through these holes the animal puts out a number of feelers like threads of jelly, and in these entangles particles of food, and draws them into itself. Now, do we anywhere to-day find these tiny shells in such masses as to build up rocks? We do. The sounding apparatus, with which we measure the depths of the sea, is so constructed as to bring up a specimen of the sea bottom. This has been used in the Atlantic, and it is found that the really deep sea bottom, too far out for rivers and currents to bring sand and mud from the land, is covered with a white mud or ooze. And the microscope shows this to be made up of an unnumerable multitude of the tiny shells of foraminifera. As the little creatures die in the sea, their shells accumulate on the bottom, and in time will be pressed into a hard mass like chalk, the whole being cemented together by carbonate of lime, in the way we explained in describing the making of limestones. So we find chalk still forming at the present day. But what ages it must take to form strata of solid rock of such tiny shells! And what a vast period of time it must have required to build up our chalk cliffs and downs, composed in large part of tiny microscopic shells! With the foraminifera the microscope shows in the chalk a multitude of crushed fragments, largely the prisms which compose bivalve shells, flakes of shells of Terebratula and Rhynchonella, and minute fragments of corals and Bryozoa. Scattered in the chalk we shall also find larger shells and otherremains of the life of the ancient sea. The base of the cliffs and fallen blocks on the shore are the best places to find fossils. Much of the base of the cliffs is inaccessible except by boat. The lower strata may be examined in Sandown and Compton Bays, and the upper in Whitecliff Bay. A watch should always be kept on the tide. The quarries along the downs are not as a rule good for collecting, as the chalk does not become so much sculptured by weathering.

The deep sea of the White Chalk did not come suddenly. In the oncoming of the period we find much marl—limy clay. As the sea deepened, little reached the bottom but the shells of foraminifera and other marine organisms. How deep the sea became is uncertain: there is reason to believe that it did not reach a depth such as that of the Atlantic.

It is difficult to draw the line between the Upper Greensand and the Chalk strata. Above the Chert beds is a band a few feet thick known as the Chloritic Marl, which shows a passage from sand to calcareous matter. It is named from the abundance of grains of green colouring matter, now recognised as glauconite; so that it would be better called Glauconitic Marl. It is also remarkable for the phosphatic nodules, and for the numerous casts of Ammonites, Turrilites, and other fossils mostly phosphatized, which it contains. This band is one of the richest strata in the Island for fossils. It differs, however, in different localities both in thickness and composition. It is best seen above the Undercliff, and in fallen masses along the shore from Ventnor to Niton. It is finely exposed on the top of Gore Cliff, where the flat ledges are covered with fossil Ammonites, Turrilites, Pleurotomaria, and other shells. The Ammonite (Schloenbachia varians) is especially common. The sponge (Stauronema carteri) is characteristic of the Glauconitic Marl. As the edge of the cliff is a vertical wall, none should try this locality but those who can be trusted to take proper care on the top of a precipice. When a high wind is blowing the position may be especially dangerous.

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