Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/510

From Wikisource
Jump to navigation Jump to search
This page has been validated.
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 grauwacke;[1] a name perhaps the more liable to misapplication as it is somewhat indefinite.

  1. If the reasons which I have ventured to suggest for the propriety of considering the dunstone 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 accurate 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 mountain groups of Cornwall may have contributed to give rise to this opinion? This character however they appear to possess in common with the Hartz, in which Professor Jameson states the clay slate to rest immediately upon the granite.