166 THE GEOLOGICAL AGE OF CENTRAL AND "WEST CORNWALL. 



h. — The ivaters were so strongly impregnatei ivith chemical 

 solutions — from mineral springs preceding the granitic irruptions 

 — that nothing could live. If this were the case, the sediments 

 would also be highly charged with chemical substances, and the 

 subsequent segregation of these substances into fissures formed 

 at a later date has given us the more recent lodes of Cornwall. 

 This we are inclined to accept as the true reason. 



The Foivey Beds. (Upper Silurian ?) 



These rocks, which were spoken of in the former paper as 

 Upper Silurian with a query, do, we believe, pass upward in 

 an easterly direction into the Devonian rocks of Polperro and 

 L008. To us it seems likely that the western portion near Fowey 

 may be Upper Silurian, the central portion about Looe and 

 Polperro Lower Devonian, while the Plymouth limestones are 

 recoo-nized as Middle Devonian. De la Beche himself speaks^' 

 of the difficulty of getting a really good line of demarcation 

 between the Silurian rocks and the Old Ped Sandstone of South 

 Wales and Hereford. A similar difficLilty has confionted 

 Professor Hull, who is driven to the conclusion that " The so-called 

 Lower Old Red Sandstone of Scotland with its fish remains, is the 

 lacustrine representative of the Upper Silurian rocks.] 



It is quite probable that we hare in these beds the geo- 

 logical equivalent of all the rocks of the typical Silurian area, 

 from the lower Ludlow up to and beyond the Passage-beds and 

 the " Tilestones " of the Devonian— and the equivalent also of 

 the Devonio-Silurian system of Prof. Hull, (v. Q.J.G.S., 

 May, 1882.) 



Against the identification of these rocks as Upper Silurian, 

 Mr. Somervail, in his paper, published by the Eoyal Institution 

 of Cornwall (Jour. Roy. Inst. Cornwall, vol. VII) brings forward 

 the authority of Mr. Peach, and says further that "they are 

 charged with typical forms belonging to both the Lower and 

 Middle Devonian." On this point it may be as well to quote 

 Mr. Peach verbatim. "1 venture therefore now to express 

 my long-formed opinion, from a most anxious consideration 

 of the question, that the Old Eed Sandstone is found at 



* Mem. Geol. Survey, Vol. 1, p. 69. 



t Hull. Proc. Geol. Soc. A'o. .383, 1880. 



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