On the Unconformities between the Rock-systems underlying the Cambrian Quartzite in Shropshire

Open Access
Publisher Website
Google Scholar
Abstract
I ntroduction A bout twelve years ago I devoted some attention to the Archæan rocks of Shropshire, and a commnnication on the subject appeared in the Quarterly Journal (1879, vol. xxxv. p. 643). Additional results were published in the numbers for May, 1882 (vol. xxxviii. p. 119), and November, 1886 (vol. xlii. p. 481). Some details, however, remained for settlement. Of these the most important is the relation between the great volcanic system (Uriconian) and the vast series of sediments which takes its name from the Longmynd. Ten years' additional experience amongst the Archæan rocks has given me some advantage in reviewing my old evidence, and recent criticisms by Prof. Blake call for some notice. The following is a summary of my published conclusions, with Prof. Blake's objections:— i. The volcanic rocks (Uriconian) of the Wrekin and Caer Caradoc are older than the Longmyndian. Prof. Blake admits that they are older than the upper part of the Longmyndian, but contends that they are not older than the lower part of that series. He accordingly separates the Longmyndian into an upper member (Cambrian) and a lower member (Monian). He furthermore expresses the belief that in one locality (Pontesbury) the felsites regarded by me as pre-Longmyndian are really intrusive in rocks which he considers Cambrian. ii. The granitic and gneissic rocks (Malvernian) of the Wrekin and other Salopian localities are older than the Uriconian, since they furnish rounded fragments to Uriconian conglomerates. Prof. Blake, on the other hand, holds

This publication has 0 references indexed in Scilit: