Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/250

156 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 13, although he allows that this is most likely much too great an estimate. We may safely say, however, that the total thickness is some thousands of feet.

The spot that yielded the jaw of Hyperodapedon, the first and, as yet, the only fossil of the "New Red" of Devonshire, is on the left bank of the Otter, just above its mouth, where the sandstone is somewhat brecciiform. The specimen was in a large block which had fallen from the low cliff that bounds the estuary, and was found by my friend Mr. J. Reid, of Canterbury, and myself.

The stratigraphical position of the fossil is therefore the lower part of the uppermost bed of sandstone (No. 3 of section), and consequently it belongs to the upper part of the formation.

That the upper part of the "New Red" of this county belongs to the Trias is clear from its passage upwards into the Lias; and as the different divisions seem to succeed each other conformably, we are led to infer that they all belong to the same formation, although the lowest division is more like the Permian of some districts. Mr. Pengelly has gone into the question of the age of the breccia of Teignmouth &c. in detail*; and it will be well to give the leading points of his argument, which are as follows, to state them in as few words as possible:—

The Dartmoor granites are thought to be of three different ages, the newer cutting through the older. All of these send veins into the Carboniferous rocks, and are therefore newer than that formation. Fragments of all three granites have been found in the "New-Red" breccia. Therefore, between the time when the Carboniferous rocks were consolidated and the time when the "New Red" began to be deposited, the following events must have taken place:— 1. All the three sorts of granite must have been successively formed. 2. The thick crust above them must have been denuded to allow of pebbles being worn out of them. These things must have taken vast time —time so great as to make it very unlikely, if not impossible, that even the lowest part of the red rocks can be Permian.

The above reasoning seems conclusive, as far as it goes, and indeed can only be shaken by attacking the data on which it is founded. One of these data is a tacit assumption that there was no very great time, geologically speaking, between the close of the Carboniferous and the beginning of the Permian period. My colleague, Mr. Hull†, has since shown, however, that in Lancashire and Yorkshire there is a great unconformity between the rocks of those ages, and that the Carboniferous rocks have in parts been denuded to the extent of very nearly 10,000 feet in vertical thickness, and perhaps at one part to the extent of more than 19,000 feet, before the deposition of the Permian beds. When it is remembered that this great denuda-

to the Devon. Assoc. of Lit. Sci. & Art, 1867.
 * Trans. Plymouth Inst. for 1861-62, pp. 27-30, and Presidential Address

† Quart. Journ. Geol. Soc. vol. xxiv. pp. 327-329.