618 KEPORT— 1886. 



In the Permian time terrestrial conditions probably prevailed over a large part 

 of Britain. It is extremel}- difficult to ascertain the exact circumstances under 

 which the Permian beds of Central England were deposited, but I should think thev 

 imply a return to physical conditions not unlike those of the Old Red Sandstone, 

 though perhaps the marine fossils which have been found in Warwickshire may 

 indicate that the water there had some imperfect connection with the sea. I 

 must not discuss the vexed question of the age of the Pennine chain, but must 

 content myself with expressing my opinion that, at most, it can only, as yet, have 

 very partially interrupted the continuity of the water in Northern England. The 

 beds there appear to indicate a supply of materials from the north and north-west, 

 as if the old rivers had not been wholly diverted by the great earth-movements 

 which closed the Carboniferous period. Sir A. Ramsay's view, that the water in 

 which the dolomitic limestone was deposited was more or less cut off from the 

 open sea, seems to me by no means improbable ; in any case, it is a rather excep- 

 tional formation, and over the greater part of Britain, probably, land sculpture 

 continued, and deposition was on the whole local. 



With the Trias a new era commences ; physical features had been now pro- 

 duced, which, in all probability, endured through a considerable part of Mesozoic 

 times. The facts which I have laid before you, regarded in the light of the general 

 principles indicated above, compel us to look away from the immediate vicinity for 

 the bulk of the materials, coarse and fine, of which the northern Trias is com- 

 posed, though neighbouring hills may have furnished occasional contributions, 

 especially to the earlier deposits. Tlie analogy of the Old Red Sandstone, the 

 Calciferous Sandstone of Scotland, and the Nagelflue and Molasse of Switzerland, 

 together with other peculiarities too well known to need repetition, make it in the 

 highest degi-ee probable that the Bunter beds were not deposited in the ocean.* 

 Hence they must be either deltas formed in an inland sea or in a lake or true fluviatile 

 deposits. Neither lake nor inland sea appears likelj' to have been sufficiently large 

 to admit of waves or currents capable of either rounding the pebbles or trans- 

 porting the materials. We are therefore compelled to fall back upon the action ot 

 rivers. The sandy beds of the Bunter indicate a stream flowing i'rom one-third to 

 half a mile an hour, the pebbles one from two to three miles ; that is to say, the 

 Upper and Lower Bunter sandstones would require the former rate of movement, 

 the Pebble Beds the latter. Now, we must remember that, in the West Central 

 district, the Lower Trias consists of three wedge-like masses, about 100 miles in 

 length, of which the coarser is probably the more extensive. The comparative 

 uniformity of the deposits in each case indicates a uniformity of flow, and suggests 

 either a large and broad stream, not liable to much variation, or one which, when 

 flooded, quickly made a channel of its valley and deposited mainly at such season. 

 I have the gi-eatest difficulty in understanding how a current of the requisite 

 velocity could be maintained by the water of a river or rivers flowing into a lake 

 or an inland sea, or in explaining the tripartite arrangement of the beds on the 

 hypothesis that a basin was gradually filled up from the northward by a stream 

 which, like the Rhone at the upper end of the Lake of Geneva, gradually advanced 

 its delta by flowing over the materials which it had previously deposited in the- 

 basin. Hence I believe that we must regard the Bunter beds as sub-aerial 

 deltas, analogous to the conglomerates in the Siwalik deposits of India,^ and to the 

 sandstone and nagelflue on the outer zone of the Alps, deposits in all respects 

 very similar to the English Bunter. We may suppose, then, that rivers emerging 

 on each side of the Pennine chain from a mountain land first formed the Lower Bunter 

 sandstones, then, owing to increasing upheaval in the mountain district, and corre- 

 sponding depression in the lowlands, flowed more swiftly so as to cover this deposit 

 with the Pebble Bed, and lastly, as its former conditions returned, laid upon. 

 this the Upper sandstones. I have spoken, for the sake of clearness, as if these 



' Compare also the Bunter and Keuper in the region traversed by the German 

 Rhine. 



^ The analogy of the Indian conglomerates was suggested to me by Dr. Blanford. 

 See Geol. Mag. Dec. 2, vol. x. p. 514. 



