of the Chalk Rock fauna confirms the above inference, for it abounds. in Gasteropoda and recalls that of the Chalk Marl. If the depth of the water over Hampshire had increased to 700 or 800 fathoms during the epoch of the Ter. gracilis zone an uprise of the southwestern land may have brought its coast line within 100 miles without decreasing the depth of water by more than 100 or 150 fathoms, and without bringing the eastern shore of the Cretaceous Ocean any nearer our area because the upheaval may have been a tilting movement only lifting the western islands.

From this time we seem to be following the progress of a great and extensive subsidence. The grains of glauconite become smaller and fewer and eventually die out altogether; the same may be said of the detrital minerals, only a few minute angular particles of quartz being found in the higher beds of the Upper Chalk, quite invisible in a slice even under a half-inch lens. Arenaceous Foraminifera are also absent except Ammodiscus incertus.

The mere thickness of deposit above the Chalk Rock amounts to 200 fathoms in the Isle of Wight, and the fineness of the material shows that its accumulation was very slow. Its other characters indicate distance from Continental land and a considerable depth of water. At the same time the deposit is purely calcareous and shows no tendency to pass into a Red Clay; this however is due to the absence of volcanic material and is not a reliable indication of depth, for Globigerina oozes, with over 90 per cent. of Calcium Carbonate, occur in the South Atlantic at depths of about 2000 fathoms. It is, therefore, quite possible for a purely calcareous deposit to be formed at that depth.

It has been asserted that Coral-mud is more like Chalk than any other modern deposit, but the resemblance is probably quite superficial. Dr. J. Murray describes Coral-mud as always containing the debris of reef-forming organisms, such as Corals, Calcareous Algæ, Echinoderms, Alcyonaria, Pteropoda, small Gasteropoda, and other Mollusca. I need not say that such an assemblage is not to be found in any part of the Chalk. The only bed which presents any approach to such a structure is the Chalk Rock, but few corals and no Alcyonarians or calcareous Algae have yet been observed in that. Prof.

Agassiz, who has examined both Chalk and Coral-mud, has no hesitation in saying that "Chalk is certainly not derived from the disintegration of Coral-reefs."*

The White Chalks agree with the Globigerina and Pteropod oozes in containing Coccoliths and calcareous spheres; they differ from both in containing fewer perfect shells. The most highly calcareous Globigerina oozes of the present day are crowded with, and often almost entirely made up of, Globigerina shells, while the more purely calcareous Chalks consist mainly of fine calcareous dust, and the single calcareous spheres are always more abundant than the Globigerinæ. This difference, however, may be due to the fact that we only possess samples of the highest layer of the modern oceanic ooze, this layer naturally consisting largely of fresh Globigerina shells. In deeper layers the fine material resulting from the decay and disintegration of the shells is likely to be more abundant, and such a deposit would greatly resemble Chalk.

While, therefore, no exact modern counterpart of Cretaceous Chalk has yet been discovered, yet it is a fact that certain arieties of Globigerina ooze resemble Chalk more than any other modern deposit, and I think we may reasonably infer that this similarity implies the existence of similar physical conditions.

*Three Cruises of the "Blake," vol. i.,

p. 148.

G

SOME NEW SECTIONS IN THE HESSLE GRAVELS.

BY F. FIELDER WALTON, F.G.S.

(Read June 8th, 1894.)

INTRODUCTORY.

Some excavations recently made at Hessle have exposed several sections of considerable interest, especially to those geologists who are studying the glacial deposits of East Yorkshire.

The sections uncover a series of gravel and sand in which mammalian bones are found; this gravel is banked up against a very steep face of chalk, the whole being overlaid by a layer of boulder clay, which covers up both the chalk and the gravel, so that upon the surface there is no indication of the strata below.

Before describing the new sections it would be well to mention what has been said about the Hessle gravels by previous writers. In the memoir of the Geological Survey these beds are placed and described among the interglacial beds of Holderness. By Professor Phillips they were thought to be pre-glacial and much older than the marine beds. Their exact place has not yet been satisfactorily determined except at a point a little to the North of Bridlington, where the buried cliff of chalk joins the present coast line. The deposits found banked against this cliff were here proved by Mr. Lamplugh to be pre-glacial. The Geological Memoir says:-" Leaving Bridlington the deposits banked against the old cliff are entirely unknown until we reach the Humber. Here, at Hessle, is the wellknown gravel originally described by Professor Phillips, and considered by him to be pre-glacial. The most striking feature of this neighbourhood is the steep slope of the chalk towards the Humber, forming what is commonly called Hessle Cliff; though it is by no means vertical. On this lies irregularly the mammaliferous gravel, covered and overlapped by boulder clay." Then two sections are given, one just west of Hessle Station showing Purple Boulder Clay, 10 feet; below this bedded sand with chalk, looking very like an old run of the hill, with chalk at the base. The other, which is one hundred yards north and close to the line, shows about eight feet of

boulder clay lying upon six inches of bedded sand; below the sand is four feet of chalk rubble, then chalk. It is to be noted that the thickness of the gravel and sand on this south slope of the Chalk is only a few inches, perhaps a little more in places. The bones mentioned by the Geological Survey belong to Elephas primigenius, Rhinoceros, Cervus, Bos, and Equus caballus. The Memoir mentions that "there is not only a north and south slope of the Chalk but also an east and west irregularity, probably an old channel connected with the Humber."

THE OLD CHALK CLIFF.

It is with the deposits banked against this east and west slope of the Chalk, together with the slope itself, that we are concerned at present, and I hope to show that they are of very great importance in arriving at a correct knowledge of the Hessle gravels; in fact I think they go a long way to prove that the Hessle gravels are the deposits that were banked up against the Humber end of the old cliff which formed the boundary of the Bay of Holderness in preglacial times; and that the east and west irregularity of the Chalk mentioned by the Geological Survey was in reality the old buried cliff. The accompanying map shows that portion of Hessle lying a little to the west of the village, and with the Humber on the south. The surface rises from the water towards the north to a little over one hundred feet. The south edge of the gravel is about twentyfive feet above high-water mark. The bridge crossing the railway in Wold Field Lane is fifty feet.

The point marked A is about ninety feet. The one hundred feet contour passes from the N. W. corner of the field in which A is marked through the N.W. corner of the Town's Pit. From this contour line the land falls towards the E.S.E., so that the twenty-five feet contour lies just to the east of the road leading from the Station. to the Village. For some miles further to the east the land is a low level, being only a few feet above the water line. The position of the Chalk is shown on the map, the actual exposures being also marked. There is an old pit just south of the railway showing about thirty to thirty-five feet of Chalk; it can also be seen in the railway adjoining. This section is on the south slope of the hill.

The Chalk does not come quite to the surface, but is covered by eight to ten feet of boulder clay. It is in this locality that the sections mentioned by the Geological Survey were seen.

A little further to the north is a large pit (Hearfield's Pit) entirely in Chalk. This is excavated to a depth of seventy to eighty feet. On the north side of the Ferriby Road is the Old Town's Pit, showing from twenty to thirty feet of Chalk. In the pit marked A, about ten to twelve feet of Chalk can be seen. It has also been exposed where the two dots are placed on the line AB. All these exposures are in the Middle Chalk, and show well-marked lines of large flints of a rather light colour. The dip of the Chalk is a little to the east of south, and is only a few degrees in amount. The Upper Chalk without flints is entirely absent. In all the sections north of the railway the Chalk comes close up to the surface, being only covered by a thin layer of boulder clay. The upper layers of the Chalk are broken up by weathering into a coarse rubble, the finer material being near the top, and gradually becoming more massive in descending. The weathering generally extends to a depth of two or three feet, in places a little more. In the pit marked A it is checked rather abruptly by a thick band of flint.

The exposures just described are, I think, sufficient to justify me in marking the position of the Chalk as I have done on the map. I must now state that to the eastward of the line which shows, I believe, the position of the Old Chalk Cliff, the Chalk is at least from thirty to sixty feet below the surface; probably sixty feet is the most nearly correct. The amount and direction of the dip will not account for this sudden disappearance of the Chalk. Of course it might be said that this would indicate a line of fault, but as the existence of the line of cliff is known to the north of Bridlington, I cannot help but think that this is the Humber end of the same cliff, more especially as there are no other indications of any great dislocation in the Chalk, although local contortions and small faults do exist, but these are more common in the Lower Chalk. Even if it does show a line of fault, it might at the same time have formed the old cliff provided that it was at least as old as Pliocene times. At a point along the line AB there is a narrow trial pit about seven to eight feet deep,