THE GEOLOGICAL STRUCTURE OP SOUTH CORNWALL. 81 



of these Ladock Beds may not be far from — or even form the 

 base of the Devonian." In the following paragraph on the 

 same page he says, " I think we are fully justified in regarding 

 these Ladock rocks simply as an upper portion of the Lower 

 Silurian." Finally, on the same page, the last paragraph, he 

 says, " altogether I think it will be very clear to any physical 

 geologist that, instead of these Ladock Beds forming as stated 

 by Mr. Collins, ' the most recent stratified rocks of Central and 

 "West Cornwall,' they are in reality about the lowest in the 

 county." 



How can these contradictory statements about one and the 

 same series of beds be reconciled ? How can beds be at once 

 (1) "the lowest in the county," {i.e. as low at least as the 

 Llandeilo beds even according to Mr. S.) ; (2) " an upper 

 portion of the Lower Sihirian ; (3) " the base of the Devonian." 

 Surely further comment on this point is needless. 



2. — The Penryn "gneiss." Referring to this rock my 

 words were as follows — "Aband of what appears to be true 

 gneiss nearly half-a-mile in width, has also been developed in 

 these Pre-silurian rocks near Penryn — close to the junction of 

 the killas and granite." Specimens of the rock were deposited 

 in the Museum of the Royal Institution, and the exact locality 

 was pointed out by Mr. Clark, who had frequently been my 

 geological companion in that neighbourhood. Mr. Somervail 

 says (p. 264) " the occurrence of a true gneiss is a state- 

 ment to which we take exception."* 



Mr. Somervail calls it a much metamorjphosed rock, and 

 refers its metamorphism to the action of the neighbouring 

 granite. Without accepting this theory as to its origin, I, of 

 course, agree that it is metnniorphic — all modern geologists 

 regard gneiss as metamorphic I believe — the question therefore 

 narrows itself to the "aspect" and name of the rock in question. 

 After Mr. Somervail's flat denial of my statement had been read 

 at the Meeting of the Eoyal Institution, and printed in the 

 newspaper reports of that meeting, I set to work to analyse 

 the rock (I had previously examined microscopic sections of it). 



* In Mr. Somervail's orifjinal paper the words were, " it approaches in no 

 way whatever the aspect of a true gneiss, from which it is readily distinguishable 

 even at first sight." See lloynl Cornwall Gasu<<tf, January 2(jth, 18H3. I am 

 glad to see that Mr. S. has been induced to tone his words down a little. 



