land by a shallow estuary about eight miles long, of variable breadth, but nowhere more than two-thirds and often less than a quarter of a mile wide, which is known as "the Fleet" or "Backwater" (Plate XV.); and for the remaining two miles, nearest to Portland, it has the sea on either side. It is with the last ten miles that we are now chiefly concerned, and to this part the following paragraph refers. The average width at the base is 170 yards near Abbotsbury, and 200 yards at Portland. The height increases from N.W. to S.E, but the inclination of the crest is not uniform. At Abbotsbury, the crest is over 22 feet, and at Chesil over 42 feet high. Borings made down to high-water level, and sometimes lower, passed through nothing but beach (except at one place, where clay was met with deep down): ten or fifteen feet from the surface, the shingle was generally mixed with a little sand, and the quantity of the latter increased with the depth until the whole was found to be very compact. (Coode.) The largest pebbles are at the eastern end, and gradually decrease in size westward, until near Burton the beach consists of sand and very fine shingle. The accompanying map will make the above description clearer. (See Plate XIV.) Westward from the end of the Bank the coast gradually gets higher, and soon there are high cliffs of Liassic, Jurassic, and Cretaceous beds. These cliffs are cut through at Burton and Charmouth by valleys with small streams, such as the Char and the Bredy, which, of course, flow seaward, that is in a south-westerly direction. These streams (excepting the Bredy) do not breach the shingle of the bays where they flow into the sea, but turn eastward (the direction of the general set of the current) for a short distance, between the beach and the land, and then filter through the shingle. There is an interval of some miles between each of these successive streams, in which the cliffs are not breached by valleys, or only by such as are cut off at some height above the sea. On the other hand, along the low shelving shore eastward of Abbotsbury, the least approach to a cliff is a great rarity, and a cliff ten feet high is a marked object: here, therefore, the streams are much closer together, each hollow in the ground sending in its share of water to the still channel of "the Fleet." Let us think now what would happen if in former times this latter part had been in the normal state of a beach skirting a low coast. The streamlets flowing down the small valleys would act just as those on the coast to the westward do; that is to say, they would turn eastward for some distance before filtering through the shingle, and most likely they would run the further between the beach and the mainland, by reason of the former being so much broader, higher, and more compact than it is on the coast. Now, as the streams are near together, instead of being separated by miles of unbreached cliff, it is quite possible (and we think most likely) that some stream might continue its easterly course between the shingle and the shore, until it reached the next stream. This might take place with several streams, where two were near together, and the increased force of two united would give the resultant stream greater power to continue its eastward course and to join on to the next. The consequence of the continuance of this process would be, that all the streams would at last join to form one long channel between the beach and the mainland, as in the subjoined Woodcut, which is on a larger scale than the Map (Plate XIV.), with the streams continued to the beach. NW. دالاد Sea S.E. Plan of streams flowing to a shore where there is a current chiefly in one direction. It seems well within the limits of possibility that this body of water would have power enough to keep its channel free, and to prevent the firm compact shingle from being driven back against the mainland. In this case the land would be protected from the cliffforming action of the sea, but on the other hand would be subject to the scooping action of land-waters, which would cut it back in gentle slopes, and irregularly widen the channel, according to the nature and hardness of the different beds acted on. Of course, on any theory, the Chesil Bank could not have been formed but for the existence of the natural breakwater of Portland; and, according to the theory now brought forward, either the narrow neck of land which must once have connected Portland with the mainland, has been breached by some means or other, inwards towards Weymouth Bay (instead of the beach being breached outwards to the sea); or, on the other hand, if at first the beach was broken through, and the stream flowed out to the sea in a southerly direction, that breach must have been slight enough to have been filled by the heaping up of shingle, when the land in its rear was worn away and Portland was separated from the mainland. As the connecting isthmus must have consisted of Kimmeridge Clay, its destruction would be no hard matter to the sea on one side (N.), and the stream on the other; and as large breaches in the Chesil Bank are known to have been refilled in a very short time, there is, perhaps, no great difficulty in accounting for the phenomena on either supposition. The destruction of the land between Portland and the mainland on the north, has been made easier by the beds having been thrown into a sort of arch, with a sharp northerly and a gentle southerly dip; the arch being of course the form that helps denudation, both by fissuring the beds, and by giving them a tendency to fall outwards. In this particular case, moreover, the lower beds that have been brought to a higher level by the said arch, so as to be within reach of denuding actions, are of a softer and more destructible kind than those that overlie them. There are three facts that seem to confirm the theory that the channel in the rear of the Chesil Bank has been formed since the heaping up of the shingle:-they are (1) that the isolated part of the bank is also the largest and strongest, the best able both to withstand the sea, and to stop the streams from flowing directly into the sea (2) that the very irregular shape and cliffless character of the shore of "the Fleet are not such as one would expect to be caused by the action of the sea along such a coast, whilst they are just what should be produced by the action of streams: and (3) that the Channel ends where the streams end. Westward of Abbotsbury, where there are no streams, the beach is not separated from the land; eastward of Abbotsbury, where there are streams, the beach is separated from the land. Whether there may have been a slight rising or sinking of the land during the formation of the beach, would we think make little difference, on the theory which we have brought forward. Whilst we are far from asserting dogmatically that the Chesil Bank must have been formed in the way described, yet we think that our theory, or explanation, involves less supposition, and tallies more with observed facts, than any other does, and that, therefore, it should be accepted until replaced by a better, or disproved. Lastly, we wish to draw attention to the confirmation given to the theory of Subaerial Denudation by our explanation of the origin of the Chesil Bank. It was not until we were convinced of the truth of the former that we saw our way to the latter; but when we began to see how great has been the share of rain and rivers in wearing away the land, and in cutting out hills and valleys, then we were enabled, by the new light thus gained, to explain the origin of a very uncommon phenomenon, which before we could not understand or account for. What had previously been a mystery, and looked like a freak of nature, became clearly intelligible, and was seen to be the natural result of ordinary causes and existing agencies. Postcript. In the discussion of this paper, Mr. J. Evans, F.R.S., suggested that tidal action may have assisted materially in the formation and widening of the Fleet." This we are far from denying, although we omitted to notice in our paper the assistance that may have been given by that action when it was enabled to come into play. II. ON A RAISED BEACH AT PORTLAND BILL, DORSET. By W. WHITAKER, B.A. (Lond.), F.G.S., of the Geological Survey of England. [PLATE XIV.] [A paper read before the Geological Society of London, May, 26, 1869.] N 1850, Mr. H. W. Bristow recorded, on sheet 17 of the Geo 66 "recent stone" at Portland Bill.-(See Plate XIV. herewith.) In 1852, Mr. C. H. Weston,' noticed the occurrence of a "marine shingle-bed" on the top of the cliff, in the following words: "This remarkable bed consists of beach-pebbles (with a few chalk-flints), rounded by continued sea action. The quarrymen said it extended about a quarter of a mile north of the Bill." In 1860 this shingle was again noticed in Mr. R. Damon's "Handbook of the Geology of Weymouth and the Island of Portland," and the occurrence of "comminuted shells" recorded. 2 Mr. Bristow has suggested to me that the shingle-bed may have been formed by the sea dashing up pebbles from the shore below, as he has known it to do in stormy weather; but I doubt whether that action is enough to cause so large a deposit. At all events it will not do so altogether, as the shingle is in part protected from such action by a thick covering of subaerial origin. Mr. Bristow tells me that, as far as he remembers, there was no good section of the deposit at the time of his visit, which must have been before 1850. The southern side of "Cave Hole" is the most northerly point of this beach, which is there thirty or forty feet above the sea, and about three feet thick, being capped by a good thickness of angular "head" (the waste of Purbeck and Portland beds), and consisting of pebbles of limestone, flint, and chert. Just southward is a projecting cave-worn ledge, with a rounded water-worn surface of Portland Stone bared of the old beach. The next projection shows a little of the same, but with pebbles and shells conglomerated together into a hard mass adherent to the surface of the stone, the shells being chiefly Littorina littorea, but Littorina littoralis and Patella vulgata also occurring. Further southward there is less of the "head," indeed hardly any, but there are remains of very small shallow pits, most likely dug for sand, as a small hole close by passed through two or three feet of clayey soil and more than three feet of coarse sand with shells, which, as far as one can judge from position, overlies the shingle. The old beach ends, after a course of less than 250 yards, before reaching the slight headland, where however there are traces of it in the soil. Continuing my southerly walk, just before getting to the Beacon at the Bill, I found shells (of the same species as those mentioned above, and also Purpura lapillus) jammed in with limestone-rubble at the top of the low cliff (as noticed by Mr. Damon). At the Bill there is a little shingle, which increases after turning westward, when the cliff rises a little. At one place a pit six feet deep shows that this shingle is sandy and bedded, whilst near by it is conglomerated into a hard mass at the top of the cliff, and further inland another pit has been dug to a depth of eight feet. Close by, at the cliff a little higher up, the shingle is covered by yellowishbrown loam (calcareous ?) with bits of stone and with land and freshwater shells (Bithinia, Pupa). A little further the latter thickens and the former thins, but both end off at the projecting spur of rock. 1 Quart. Journ. Geol. Soc., vol. viii., pp. 117, 8. I believe that it is only to the part noticed in the last paragraph that Mr. Weston's remarks refer. Postcript. In the discussion of this paper, Sir C. Lyell said that he had found in this raised beach more species of shells than those above mentioned; and Mr. Prestwich said that at one spot the number of young shells was remarkably great as compared with that of older shells. III. ON THE OCCURRENCE OF MACHAIRODUS IN THE FOREST-BED OF NORFOLK. A By E. RAY LANKESTER, B.A. Oxon. [PLATE XVI.] SPECIAL interest has always attached itself in this country to the remains of that rare and bizarre carnivor, the Sabretoothed tiger. For as yet it has only been indicated to us on this side of the Channel by the most fragmentary and unique specimens -the two teeth, incisor and canine, obtained by the Rev. Mr. MacEnery, from Kent's Hole, Torquay, the authenticity of which have even been doubted. Whilst, however, paleontologists have pretty generally come to the conclusion that these two isolated teeth are really the remains of a Devon Sabre-tooth, no further specimens have, I believe, been recorded from other caverns in this country. The forest-bed of Norfolk, which furnishes remains of Rhinoceros Etruscus in some abundance, and of Ursus Arvernensis-and other forms associated in central France with species of Machairodus—has hitherto not given up any remains of that carnivor to the energetic collectors of Norfolk. In July, by the kindness of the Rev. John Gunn, I was enabled to see some of the matters of geological interest in Norfolk, and in looking through the very beautiful collection of mammalian remains from the Forest-bed in the possession of Mr. Jarvis, of Cromer, I observed the portion of a tooth figured here. Suspecting its nature, I begged the loan of it from its owner, who very courteously complied with my request. I have since carefully compared it with the casts and specimens of the canines of Machairodus in the British Museum, and determined it as a fragment of the right upper canine of a species of that genus. The only doubt which one could possibly have about such a specimen as this, with its characteristic serrations and outline (see Plate XVI.), was that it might belong to a large Megalosaurian whose remains had been brought down from more northern Jurassic beds, and cast on the Norfolk shore. Two eminent Palæontologists to whom I shewed the fragment, suggested this account of its origin to me, whilst two others agreed in the view that it belonged to Machairodus. The known teeth of Megalosaurus are, however, smaller, and of a much more sharply curved outline, than is indicated by this specimen, |