the rocks which form the highest ground, and, which in the glacial submergence would constitute the last points remaining above water. The only agency, it appears to me, by which these enormous masses could have been transported, is that of floating ice. Some of the masses of the Marlstone Rock-bed have been carried across deep valleys, a distance of probably not less than 30 miles.

b. Glacial Gravels.-These consist of an accumulation of fragments of rock, often of considerable size, and, not unfrequently, retaining their glacial markings; they often exhibit the most. remarkably contorted stratification. Their materials are almost identical with those of the boulders in the Boulder Clay, consisting of rounded fragments of hard chalk, often in prodigious abundance, angular flints, masses of Oolitic, Liassic, and Carboniferous rocks with some from older formations. Indeed these gravels might aptly be described as Boulder Clay in which, from the action of some local cause, the argillaceous matrix has not been deposited. These gravels are in some places seen to be actually interstratified with the ordinary chalky Boulder Clay, and at times to pass insensibly into it; while they are often found, through denudation, capping hills of Boulder Clay; they are quite as often found underlying a great thickness of that deposit. It is an interesting and significant circumstance, that in the western parts of the district, where the glacial series occupies the highest grounds, these gravels acquire great importance, while in the eastern part of the area they are generally confined to thin seams and patches in the midst of the Boulder Clay. Probably we should be right in regarding the glacial gravels as exhibiting the littoral condition of the Boulder Clay.

Sometimes these beds of gravel are very violently contorted, exhibiting evidences of just such lateral pressure as would be produced by the grounding of icebergs. A good typical section of these greatly contorted glacial gravels is exhibited in the large pit between Whadborough and Ouston. (See Fig. 19, p. 248)

As is well known, similarly highly contorted beds are not unfrequently found in the midst of the Glacial Series, as in the cliffs of Norfolk, Suffolk, &c. These remarkable appearances have been variously interpreted in different cases; by the grounding of icebergs, the thrusting up of ice-floes on a shelving coast during storms, and the melting of great masses of ice, enclosed in the deposits of mud and sand.

Although some geologists have attempted to show that the great glacial formations composed of clay, and sand or gravel, respectively, belong to perfectly distinct periods and mark different climatal and physical conditions in the Midland district of England, and even entire changes in the disposition of the land and sea of the period; yet nothing can be clearer that in the area we are more particularly describing the beds of glacial clay, sand and gravel, replace one another in the most capricious manner, and are evidently dependent on the action of causes of extremely local character.

Fig. 19. Pit in Glacial Gravels between Whadborough and Ouston.

6

ዝ

a. Boulder Clay.

d, h. Coarse gravel. b, e, g, l, n. Fine gravel.

c, f, k, m. Sands. i. Loam.

a red colour, and with much false bedding, sometimes, as near c. Glacial Sands. --These are coarse, siliceous sands usually of

Pickwell, attaining a considerable thickness and being interstratified with the other glacial deposits. Their relations to the Boulder Clay are identical with those of the last described beds, into which, indeed, they sometimes pass by insensible gradations.

C. POST GLACIAL DEPOSITS.

In this group we include all those masses of material, which, from actual superposition, or from the fact of their containing derived fragments of the glacial beds, are inferred to be of later date than the last mentioned.

a. Cave Deposits.-The facility with which all limestone rocks are hollowed into caverns by the solvent action of subterranean waters is frequently illustrated in this district; but the rapidity with which the Oolitic rocks undergo denudation has probably, in most cases, prevented such caverns from being the means of preserving the exuviæ of extinct animals like the great caves of the Carboniferous and other older and harder limestone rocks. The only point within the limits of Sheet 64 at which a cavern has been found is at Tinkler's Quarry near Stamford. Here, during the quarrying operations about 30 years ago, a small cave was met with, the earth on the floor of which contained the teeth and bones of Carnivora, Ruminants, and Elephants. All traces of this cavern, which was of no great size, have disappeared in consequence of the continued working of the quarry, and the remains found in it appear to have become scattered. Fortunately however some of them have been secured for scientific examination by the zeal of S. Sharp, Esq., formerly a resident at Stamford. These were submitted to Professor Rolleston of Oxford, who pronounced them to be as follows :-

Hyana. Teeth of two individuals.

Elephas. Portion of a tooth of a small individual.
Cervus megaceros. Tooth.

Cervida. Various remains.

The long bones appear to have been in all cases broken for the extraction of the marrow, and in some instances they exhibit indications of having been gnawed.

I was unable to obtain exact information as to the size of this cave: by some, who saw it, it is said to have been from 15 to 20 ft. square, by others, to have resembled only a large fissure. There can be no doubt that this, like the caves of Settle and Kirkdale in Yorkshire, the caves of the Vale of Clwyd in North Wales, the Gower Caves in Glamorganshire, Wookey Hole in Somersetshire, and other similar caverns, was once the den of hyenas, and that the other bones belonged to animals which had been seized and carried, by the carnivores, to their lair to be devoured.

b. Valley Gravels.--These gravels are found occupying the bottoms and sides of the existing river valleys, and in some places extending to elevations of from 40 to 50, or even a great number of feet, above the present levels of the rivers. They are at once distinguished from the pre-glacial valley gravels, before noticed,

not only by their relations to the present system of drainage, but by being composed of materials evidently derived from the Boulder Clay of the district, such as chalk flints and fragments of Paleozoic rocks, and mingled with the detritus, derived directly from the beds of the Jurassic series. The pre-glacial valley gravels consist, as we have already seen, of the latter class of materials only. It is along the valleys of the Nene and Weiland that we find the largest deposits of these gravels; but along the sides of some of the minor valleys, such as those of the Chater, the Gwash, and the Glen, fringes of similar gravels are also found. At some points, as about Elton, the passage of water through these masses of gravel has, by the solution and re-deposition of calcareous matter, resulted in the formation of indurated masses like those described as occurring in the pre-glacial gravels.

Along some of the larger valleys, these gravels may be classed as belonging to two different series, according to their elevation above the present level of the river; and these are called the high-level and low-level valley gravels.

Occasionally the valley gravels yield shells which are found to be all of a fresh-water character and belong to species still living in the rivers which now occupy the valleys. Such shells are by no means common in the valley gravels of this area, and are very local in their mode of occurrence. It is only where a thin seam of sandy loam occurs interstratified with the gravels that we have usually any chance of detecting such molluscan remains preserved.

Mammalian remains however are much more common in the district, and local collectors might probably, by watching the excavation of some of the large gravel pits of the district, obtain interesting series of such fossils. As is well known the mammalia, represented by the bones, teeth, &c. found in these gravels, include species altogether extinct and others now only found in far distant regions; and these are mingled with remains of forms still living in the area. The tusks and teeth of elephants, with the teeth of the rhinoceros, hippopotamus, hyæna, and horse, and the horns of the red-deer and urus occur in the valley gravels of this district.

These valley gravels have of late years attracted much attention owing to the discovery in them of flint implements, undoubtedly fashioned by human agency and associated with the remains of extinct mammalia. No such discovery of flint implements has as yet, however, been found within the limits of Sheet 64.

At some points, as New England, near Peterborough, the valley gravels are found to be covered by deposits of loam crowded with terrestrial shells of recent species. These loams appear to be analogous in their character, and mode of occurrence, with the continental "Loess."

c. Estuarine Gravels.-The valley gravels afford ample evidence that the existing rivers formerly flowed at much higher elevations than at present. We have also clear proof that, at the periods when

these higher level gravels were formed, the whole of the flat lands of the fens were submerged beneath the sea, and the estuaries of the Nene and Welland were at the points now occupied by the towns of Peterborough and Deeping. At some distance above these points the gravels, which form a continuation of the valley gravels just noticed and serve to form a link between them and the marine deposits of the Fenland, were of estuarine character and contain an admixture of fluviatile and marine shells. Such estuarine gravels have been found at Peterborough and at Overton Waterville. At the latter locality they have yielded Ostræa edulis, Cardium edule, Planorbis carinatus, Ancylus fluviatilis, Bithinia tentaculata, Lymnea glutinosa, Pisidium amnicum, &c. With these shells were associated the remains of Elephas primigeneus, Rhinoceros tichorinus, Equus caballus, Canis lupus, Hyæna spelæa, Cervus elaphus, Bos primigenius, &c.

d. Marine Gravels of the Fenland.-As the ordinary valley gravels graduate into the estuarine gravels, so these last pass insensibly into the marine gravels of the Fenland. In the materials of which they are composed, indeed, these several gravels are quite indistinguishable from one another, and the classification adopted for them is based on their geological relation and the nature of their organic remains. The gravels of the Fenland sometimes contain an abundance of marine shells and some marine mammalia, these being mingled with the bones, teeth, and horns of the same terrestrial species as occur in the estuarine and fluviatile gravels. The marine shells are almost all of existing species, and such as inhabit neighbouring seas; they usually present a marked littoral facies. Among those most commonly found are Cardium edule, Littorina littorea, Turritella communis, Buccinum undatum, Tellina solidula, Ostrea edulis, Mytilus edulis, Cyprina Islandica, &c. The only indication of the prevalence of climatal conditions differing from those of the neighbouring shores which I have found in these gravels, is the abundance of Cyprina Islandica, a shell which, however, occurs in sufficient abundance on the coast of Yorkshire, only a little distance to the northwards.

These marine gravels evidently formed beaches surrounding the old sea which once covered the Fenland, and they are clearly seen, not only at the boundary between the Fens and the higher land surrounding it, but forming belts round the numerous islands, composed of Oxford Clay or Boulder Clay, which diversify the surface of the former. In some cases the gravels are found extending to considerable distances below the silt and peat of the fens; and such deposits may mark the gradual extension of marine conditions over the area in consequence of subsidence. The marine gravels of the Fenland may therefore be considered as representing the littoral condition of a considerable series of deposits, among which are the silts to be hereafter noticed that were formed while the greater part of the district was covered by the sea: the small eminences which now make such marked features in the Fens, such as those occupied by the towns of