TRANSACTIONS OF THE SECTIONS. 91 



and they are clearly separated from all these older beds by another and underlying bed 

 of gravel. 



The author further noticed that the lower sands and gravels under the Boulder clay 

 contained a layer of marine shells in a perfect state of preservation, consisting of 

 Mytilus edulis (some with Balanl attached) and Littorina lilloralis, and traces of 

 others. Again, below this is a seam of dark clay containing freshwater shells, chiefly 

 the Pisidium amnicum, and a Unio, while a short distance lower is the well-known 

 Forest bed with its elephant and other mammalian remains. He concludes by call- 

 ing attention to the Mundesley deposit as being probably synchronous with the flint- 

 implement bearing deposit of Hoxne. 



On Slickensides. By J. Price. 



On the Chronological and Geographical Distribution of the Devonian Fos- 

 sils of Devon and Cornwall. By William Pengelly, F.G.S. 



The limestones, slates, and associated sandstones of North and South Devon and 

 Cornwall have, as is well known, caused much perplexity as to their real place in the 

 chronological series of the geologist. Thanks, however, to the labours of Professor 

 Sedgwick, Sir R. I. Murchison, Mr. Lonsdale and others, the problem is now gene- 

 rally admitted to be solved ; the rocks in question are the equivalents of the Old Red 

 Sandstones of Scotland and elsewhere ; they belong to what is known as the Devonian 

 age of the world. 



Some little difficulty, however, exists — or rather once existed — in the way of the 

 full and unqualified acceptance of this decision. The rocks of Devonshire are crowded 

 with the remains of invertebrate animals, especially sponges, corals, and shells; 

 whilst the supposed contemporary deposits of Scotland and the adjacent isles are so 

 rich in fossil fish, that, in the language of the late Hugh Miller, " Orkney, were the 

 trade once opened up, could supply with ichthyolites, by the ton and the shipload, 

 the museums of the world*;" but the fossils characteristic of either of these districts 

 are not found in the other. Scotland does not yield the mollusks and zoophytes of 

 Devonshire, nor is there recorded in the latter district more than the faintest trace of 

 the ichthyolitic wealth of the North. 



Though this fact may still have difficulties connected with it, they have ceased to 

 be chronological ; for Sir R. I. Murchison tells us that " The same fossil fishes, of 

 species well known in the middle and upper portions of the Old Red of Scotland, and 

 which in large tracts of Russia lie alone in sandstone, are in many other places found 

 intermixed, in the same bed, with those shells that characterize the group in its slaty 

 and calcareous form in Devonshire, the Rhenish country, and the Bouionnais." " The 

 fact of this intermixture completely puts an end to all dispute respecting the identifi- 

 cation of the central and upper masses of the Old Red of Scotland with the calcareous 

 deposits of Devonshire and the Eifelf." 



Professor Sedgwick has proposed the following threefold division of the Devonian 

 rocks of Devon and Cornwall : — 



"The first and oldest of these groups may be conveniently called the Plymouth 

 group, using these words in an extended sense, so as to include all the limestones of 

 South Devon and the red sandstones superior to the Plymouth limestones. The 

 equivalent to this group in North Devon includes, I think, the Ilfracombe and Linton 

 limestones as well as the red sandstones of the north coast. 



" The second group includes the slates expanded from Dartmouth to the metamor- 

 phic group of Start Point and Bolt Head, and is, so far as I know, without fossils: it 

 may be called the Dartmouth group, and its equivalent in North Devon is found in 

 the slates of Morte Baiy, which end with beds of purple and greenish sand-rock and 

 coarse greywacke. It ranges nearly east and west across the county. 



" The third group is not, I think, found in South Devon ; but in North Devon it is 

 well-defined, commencing on a base-line of sandstone beds which range nearly east 

 and west from Baggy Point (on the western coast) to Marwood (which is a few miles 

 north of Barnstaple), and thence towards the eastern side of the county. This group 



* Footprints of the Creator, p. 2. f Siluria, Third Edition, p. 382. 



