claiming to make known the existence of Dakosaurus in England. I trust I shall not appear wanting in courtesy in noticing the paper now, instead of waiting till it is published in full. But as I should then have no more or less to say, I have thought it better to make known the fact that Dakosaurus has already been chronicled as an English fossil, so that when Mr. Wood-Mason publishes his paper, he may withdraw his claim to be its first discoverer.

In the Woodwardian Museum occur vertebræ, limb-bones, and teeth of a reptile, for which I had used and still use the name Dinotosaurus; and, in a controversial writing on the Potton sands, I had referred teeth (in no way to be distinguished from those in the Kimmeridge Clay) to the same genus. My friend, Mr. Walker, soon after found that these teeth, which he had originally referred to as of crocodilian character, were similar to those in the British Museum, for which Quenstedt had used the name Dakosaurus, and in his next paper in the Annals of Natural History, 1866, and in the British Association Reports, he chronicles the Dakosausus as an English fossil, and acknowledges the assistance of Mr. Henry Woodward in its determination. It also was found in the beds at Wicken (Upware), and duly enumerated in a paper on that locality by Mr. Walker in 1867, in the GEOLOGICAL MAGAZINE, p. 310.

It has been known to me for several years in several species, as characteristic of beds from the base of the Oxford Clay to the sands over the Kimmeridge Clay. HARRY G. SEELEY.

WOOWARDIAN MUSEUM, CAMBRIDGE.

"MIDDLE DRIFT" GRAVEL AT LOPHAM FORD.

SIR,-My friend Mr. Gunn originally pointed out to me the interest attaching to Lopham Ford, as a crucial test on the question of denudation. He now asks, "how, supposing the valley of Lopham to be attributable to either pluvial or fluvial denudation, supposing the watershed to have been ever (? always) on that spot, could the magnificent bed of valley gravel have been deposited on the bank, near the ford and the watershed?"

What will he say, when I reply that there is no such bed of valley gravel there at all? The gravel seen is the "Middle Drift,” in which the valley is excavated. I examined it carefully, and came to that decided conclusion. As corroborative evidence I found in it a bed of whitish sand, containing abundance of the same minute organisms from the Chalk, which are so plentiful in the Glacial sand at Firgrove pit near Norwich, and in the railway cutting near Wells. These could hardly be abundant in a river-gravel in a valley not cut through the Chalk.

I need not reiterate that I do not attribute the excavation of this valley to pluvial or fluvial, but to Glacial action. The contorted condition of the superficial beds, or "trail," is extremely marked in the gravel pit on the Suffolk side at Redgrave.-O. FISHER.

HARLTON, CAMBRIDGE.

ELEPHAS MERIDIONALIS IN THE NORWICH CRAG.

Sir, I must beg you to allow me space for a few additional remarks-Firstly, Mr. Gunn's "evidence" is, I may venture to say, without offence, undeniably no evidence at all, and the way in which Mr. Fisher uses it in building a theory is an example of a common method of the growth of error. Mr. Fisher is quite right in saying that Mr. Whincopp's collection does not contain E. meridionalis, nor do other equally fine collections known to me. Mr. Fisher abandoning E. meridionalis as a Red Crag fossil, observes--"The species, however, is abundant in the Norwich Crag, which is sufficient for my argument." I would ask here, what exactly is the mode of occurrence of E. meridionalis in the Norwich Crag? How many molars have been found, and in what parts of the Norwich Crag? The headquarters of E. meridionalis in this country are undoubtedly in the Forest-beds, and the few specimens which appear to have come from the Norwich Crag, may have been derived, or have come from a representative horizon of the Forest-bed. Why does Mr. Fisher speak of "Miocenes of the south" as furnishing derivata to the Suffolk bone-bed? Surely Miocenes of the north will satisfy the required conditions better.

Some of Mr. Fisher's paragraphs lead me to suppose that I have been understood as wishing to dispute the identity of the Red and Norwich Crags. This was not my intention. I quite believe that they shade off into one another-the more northern beds of the Upper Crags being newer than the southern; this rule holding good for the various localities of the Red Crag, as well as the Norfolk Crag. My object was merely to get the facts rightly stated. The truth is, that nothing is known of the terrestial mammalia of the Coralline, or Red Crag period, i.e., of a fauna cœval with the marine fauna of those deposits, and I believe the same is true for the Norwich Crag. The contents of Mr. Gunn's stone bed have no more to do with the Norwich Crag than have the contents of the Suffolk Bone-bed (two species of Mastodon, Rhinoceros, etc., Cetacean bones and nodules of Plio-miocene age,) to do with the Red Crag. I should much like to see a list of Mammalian remains in addition to the Mastodon teeth, found in Mr. Gunn's stone-bed. The Mastodon does not occur in this country with Elephas meridionalis at all-nor in France and we may doubt if it does so even in the Val d'Arno, since the strata may have belonged to different horizons which furnished the one to the other. The relations of-1st, the Mastodonfauna of the Suffolk bone-bed and Norfolk stone-bed; 2nd, the E. Meridionalis-fauna of the Forest-bed; and 3rd, the Marine-fauna of the Crags, have still to be worked out, and this can only be done by keeping the three quite distinct and adhering to fact. I think I have clearly shown that the Mastodon, Cetacea, etc., of the Suffolk bone-bed are older even than a deposit (the sandstone nodules) containing Conus, Cassidaria, Pyrula, and Isocardia, in place of the more boreal forms of the Crags. The question arises as to whether

1 This compound is used to avoid offence.

The re

the same is true of the Mastodon of the Norfolk stone-bed. mains of the Forest-bed are in the hands of Mr. Boyd Dawkins, who doubtless will not allow them to be mixed up with Crag or Bonebed specimens. E. RAY LANKESTER. HAMPSTEAD.

SUGGESTIONS ABOUT DENUDATION.

paper

SIR,-Your number of this month (p. 109) contains a clever by Mr. Kinahan. With one exception, I agree with everything that he has said. The exception relates to what Mr. Mackintosh has dubbed "My hard-gorge and soft-valley theory." I think that Dr. Hooker's terraces are patches of alluvial plains (or river haughs) sliced into terraces, and not filled-up lakes. Alluvial plains, properly so called, are deposited by the overflow of rivers upon flat dry ground, and not in hollows like filled-up lakes. Take the engraving of Dr. Hooker's terraces.

On the left of the river, as you look at it,

Diagram of the Glacial Terraces at the Fork of the Yangma Valley (copied, slightly reduced in size, from Dr. Hooker's Himalayan Journals, vol. i. p. 219).

are four terraces. Number them 1, 2, 3, 4 from the river. No. 1 is now being formed in precisely the same way as all alluvial plains, and as all the preceding terraces have been formed. That is, by deposit from the overflow of the river on to the dry flat surface of the terrace, which also receives the waste of the sides of the valley and of the old terraces. No. 2 forms the banks of the river when in flood, and is vanishing now in precisely the same way as the preceding terraces have vanished. That is, the flooded river pulls the loose banks down, till No. 2 is driven against the side of the hill as No. 3 has been driven there. No. 1 then extends to the hill-side, and is added to by every flood till the bed of the gorge is lowered. Then No. 1 shares the fate of No. 2, 3, 4, and a new alluvium is formed at a lower level and at the expense of No. 1. Mr. Kinahan asks "what causes the barrier ?" Any comparatively hard strata which cross the stream below softer strata. Even the

soft Chalk of the North and South Downs form narrow gorges below the broad alluvial flats of the softer Weald Clay. But these Weald Clay flats are at the same level as the beds of the Chalk gorges. There are no hollows or lakes above the gorges.

The origin of all alluvial plains, properly so-called, is the stoppage of the lowering of the bed of the valley. The bed of the valley above the stoppage is then cut back perfectly horizontal at the level of the stoppage. The rain flood-water from the inclined sides of the valley is then checked, overflows and deposits on the horizontal part. The sea stops the lowering of the bed of every valley. Therefore, the parts next the sea are composed of horizontal alluvium. Take the alluvial plain of the Nile from Cairo to Syene. We know that it is raised by deposit every year. But this rising is not the result of a lake "behind a barrier." This rising of the lowest or marine alluvial plain is constant, that is, it will go on as long as the relative level of the land and of the sea remain the same, and no terraces will be formed. Parallel terraces are formed by patches of alluvial plain. That is patches formed in valleys cut in soft strata above gorges of hard strata, which make temporary stoppages of the lowering of the bed of the valley. But we do not require (as Mr. Kinahan supposes) 66 power to scoop out rocks behind a barrier" lower than the barrier. No hollow or lake is formed. The alluvial flat above the gorge is never lower than the bed of the gorge, it is at the same level, or, if anything, a shade higher. This principle accounts for the Kames at Carstairs above the gorges of the Clyde at Lanark, and of the Mouse Water at Cartland Crags, and I guess it would explain the enigma of the Eskers of Central Ireland.

GEORGE GREENWOOD, Colonel. BROOKWOOD PARK, ALRESFORD, 6th March, 1869.

MISCELLANEOUS.

GEOLOGY OF ALASKA TERRITORY.

Mr. HENRY WALTER BATES, Secretary to the Royal Geographical Society, has kindly forwarded me the subjoined extract from a letter of Mr. W. H. Dall, Smithsonian Institute, Washington, U.S. to F. Whymper, Esq., Haslemere, Surrey :-" Alaska.-You can tell your scientific friends that I have settled the geological question by fossils which I got this last year near Topanica (Norton Sound): a fine species of Platanus, which is undoubtedly Miocene Tertiary; there are no older rocks below Nuclukayette (Yukon River). The south flanks of the Alaskan range have Triassic? and Miocene Tertiary beds."-Mr. Dall's large collections are now being arranged at the Smithsonian Institute.