500 Mr. CoNYBEARE on the Strata near Clovelly. 



the marked difference between the two great varieties, which appear 

 to include by far the larger part of the stratified rocks occurring in 

 the west of England, is such, as to render it by no means desirable 

 that they should both be designated by the common name of grau- 

 wacke ; * a name perhaps the more liable to misapplication as it is 

 somewhat indefinite. 



* If the reasons which I have Tcnturcd to suggest for the propriety of considering the 

 diinstonc and shillat as of a formation distinct from that of the killas be not entirely void 

 of foundation, it is perhaps the more desirable that the attention of geologists should be 

 called to the examination of the subject, as it is understood that a large and respectable 

 body of mineralogists are disposed to apply the name of killas to those stratified rocks in 

 the northern part of Great Britain, which have hitherto been considered by the most accu- 

 rate observers as indisputably belonging to the grauwacke formation. Is it not possible 

 that the frequent, for I apprehend we are scarcely yet entitled to say the total absence 

 of gneiss and mica slate in the moantain groups of Cornwall may have contributed to 

 give rise to this opinion ? This character however they appear to possess in common with 

 the Ilartz, in which Professor Jameson states the clay slate to rest immediately upon the 

 granite. 



