THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 33 



and dip mostly to the S.E., although there are some foldings, as 

 shewn on the accompanying sections. On the north side of the 

 granite bosses these rocks thin out greatly, and are mostly 

 horizontal or very nearly so. 



The south coast crumplings were obviously produced previous 

 to the laying down of the Ladock beds. The crumpling has 

 evidently been produced by a force acting at right angles to the 

 line of strike — i.e. parallel to the line of granitic upheavals. 

 The folds were probably produced in part by these upheavals — 

 but chiefly by another axis of upheaval parallel to this granitic 

 axis now entirely submerged. This second line of upheaval was 

 probably from 25 to 35 miles to the south of the present coast — 

 it was long ago suggested by Sedgwick and Murchison,* Godwen- 

 Austen,t and others. A line so situated would pass beneath the 

 Eddystone rooks, and would account for their very high degree 

 of metamorphism. 



In my paper on the Meneage district already referred to, I 

 have brought forward evidence to prove that the Lower Silurian 

 rocks in Cornwall are at least 23,000 feet thick, and the Veryan 

 and Portholland Sections tell the same tale. 



The Ponsanooth Beds. (Cambrian ?) 



The Ladock beds have been deposited upon the denuded 

 edges of the uptilted Silurian rocks. The unconformability is 

 sufficiently proved by the manner in which the very persistent 

 and regular strike of the beds is seen to suddenly change — 

 although the actual unconformability may not be visible in many 

 clear-cut rock sections. (See, however, Eigs. 1, 2, 4, Plate A, 

 and Pig. 5, Plate B). The line of junction of the beds is very 

 frequently obscured by the occurrence of a vallej, the position 

 of which has been determined by that very junction. In such 



* " On the Physical Structure of Devonshire, &c." Trans Geo). 8oc. Lond. 

 II, V, 662; and "On the slate rocks of Devon and Cornwall. Quart. Jour n. 

 Geol. Soc. viii, 9. 



t " On the possible extension of the Co:il Measures beneath the south-eastern 

 part of England." Quart. Journ. Gtol. Soc. xii, 45. See also " The Metamor- 

 phosis of the rocks extending from Hope's Cove to Start Bay" by Mr. Peugelly. 

 Trans. Dev. Assoc 1879. 



c 



