458 



THE GEOLOGIST. 



two systems of deposits, and believing that no sufficient reason liad been 

 assigned for tlie absence of the Old Eed fish in Devon and Cornwall, have 

 never failed to cherish the belief that, sooner or later, they would be found 

 there ; and, indeed, we have heard from time to time that at length the 

 wished-for ichthyolites have been exhumed in the southern area. At the 

 meeting of the British Association held at Cork, in 1843, Mr. Peach 

 brought under the notice of the Geological Section, certain fossils w-]iich 

 had then recently been found by Mr. Couch, in the Devonian slates, near 

 Polperro, in Cornwall. The palaeontologists to whom they were then sub- 

 mitted considered them to be remains of fishes ; and, indeed, the late Mr. 

 Hugh Miller subsequently found a specimen amongst them, of which he 

 said that "if he had found it in the Old Eed Sandstone of Cromarty, he 

 ■would have no hesitation in regarding it as a fragment of some dermal 

 plate of Asterolepis." These fossils w^ere found in great numbers in cer- 

 tain localities, and extended along the Cornish coast, at by no means wide 

 intervals, from Fowey Harbour to the Eame Head ; they were constantly 

 spoken of as the " Polperro fish," and the slates in which they were found 

 as the " Polperro fish-beds." At length. Professor M'Coy and Mr. Carter 

 of Cambridge subjected them to a rigorous microscopic scrutiny, and pro- 

 nounced them to be nothing more than sponges belonging to their new 

 genus Steganodictyum, of which they formed two species, S. Cornuhicum 

 and S. Carteri. It may be doubted, however, whether certain fossils 

 found with them were not true ichthyolites ; indeed, one specimen which, 

 a few years since, I found in the Steganodictyum beds at Looe, in Cornwall, 

 has been pronounced, by Sir P. Egerton and others, to be a decided ich- 

 thyodorulite.* It has not been identified, however, even generically. 



A few weeks since, I had the good fortune to find a fossil in the Pleuro- 

 dictyum slates at Meadfoot, near Torquay ; that is, in certainly the lowest 

 group of the rocks of South Devon and Cornwall, and which Sir E. Mur- 

 chison has placed on the horizon of the Cephalaspidian and Pteraspidian 

 beds — the lowest of his divisions of the Old Eed of Scotland. From the 

 first, I believed it to be a fish-scale or plate ; and very recently, Mr. Davies, 

 of the British Museum, has not only confirmed this, but has identified the 

 fossil as a scale — or rather, a portion of one — of PJiyllolepis concentricus, 

 a fish known only by its fossil scales, and which had hitherto been found 

 only in the Clashbennie beds, belonging to Sir E. I. Murchison's Upper 

 Old Eed. 



This fossil then appears to necessitate the belief, either that the organism 

 which it represents had a greater vertical range than has been supposed, — 

 that is, that it belonged to the Lower and Middle, as well as Upper Old 

 Eed fauna, — or that the Tleiirodiotyum beds of Devon and Cornwall, in- 

 stead of being on the horizon of the Lower, are on that of the Upper Old 

 Eed series of Scotland. 



To accept the first of these, apparently the only two alternatives, would 

 be to accept the difficulty of supposing that PJiyllolepis dates from Cepha- 

 laspidian times ; that it witnessed the extinction of this family as well as 

 the subsequent introduction and withdrawal of Coccosteus, Asterolepis, and 

 others ; and yet that, unlike its early contemporaries, it failed to leave be- 

 hind any trace of its existence in the Old Eed rocks, save only in the 

 upper of their three groups. 



Eejecting this hypothesis, however, we seem compelled to adopt its rival, 

 which amounts to this :— there are in Devon and Cornwall no representa- 

 tives of the Lower and Middle Old Eed rocks of Scotland, but the 

 lowest — the Pleurodictyum beds — of the former are on the horizon of the 

 * See 'Geologist/ vol. iv. pL vi. p. S4^G. 



