THE GEOLOGICAL STRUCTURE OF SOUTH CORNWALL. 267 



the thick bedded sandstones occupy the lowest position, and are 

 well seen in the neighbourhood of Fowey. The red and purple 

 slates form a higher portion of the system, and are well exposed 

 in many of the road sections a little to the west of Polperro. 



Paleeontologically these beds are characterized by numerous 

 fish remains, likewise by the occurrence of many corals, 

 echinoderms, numerous shells representing all the great orders 

 of the mollusca, the whole fauna forming an assemblage which 

 gives the palseontologist but little difficulty in referring the 

 strata to their true geological position, viz., the Devonian, to 

 which they had been previously referred by many geologists 

 who understood the weight and bearing of their palseontological 

 evidence. 



How Mr. Collins has fallen into the error of identifying 

 these beds with the Upper Silurian, it is difficult to imagine, 

 charged as they are with typical forms belonging both to the 

 lower and middle Devonian. 



The term Upper Silurian as applied to these Fowey beds 

 must therefore be abandoned, nay, further, it is quite evident 

 that there is no representative of this formation in the whole 

 area under consideration, and indeed throughout the county of 

 Cornwall. This is a fact of some interest, as it is in strict ac- 

 cordance with the order and succession of the rocks of Brittany, 

 where the Lower Silurian and Devonian formations are both 

 present, but where the Upper Silurian is entirely absent. 



Devonian or Ladock. — Under the term Ladock, which Mr. 

 CoUins used as a synomyn for Devonian, owing to beds said to 

 be of that age receiving a typical development in the parish 

 bearing that name, is a group of strata which he regards as the 

 highest or " the most recent stratified rocks of Central and West 

 Cornwall." 



He considers that the rocks of this system have their 

 boundary a little to the south of Truro. To the north of this 

 town they cover an extensive area, stretching from coast to coast 

 as between Pentewan and St. Agnes' Head. They are described 

 as principally of a slaty character, with a few sandstones having 

 a regular east and west strike, and nearly or altogether devoid 

 of organic remains. Confining our remarks to the strata of this 

 area (excluding those on the north coast at Watergate Bay, 

 which I am not acquainted with from personal observation), let 



