UNCONFORMITIES BETWEEN BASAL KOCK-GROUPS OF SHROPSHIRE. 109 



10. On the Unconformities between the Rock-systems underlying 

 the Cambkian Quartzite in Shropshire. By Dr. Ch. Callaway, 

 M.A., F.G.S. (Read January 7, 1891). 



Contents. 



Page 

 I. Introduction 109 



II. Review of the Evidence for the respective Ages of the Uriconian and 



Malvernian Rocks 1 10 



1. The Felsites. 



(a) Church-Stretton Area. 



(b) Pontesford-Hill Area. 



2. The Alleged Unconformities. 



(a) The supposed Break in the Longiuyndian. 



{b) Presence of Rolled Fragments in the "Monian" Series. 



3. The Conglomerates and Grits. 



(a) The Cardington Massif, 

 {b) Caer Caradoc. 



(c) Charlton Hill. 



4. The Granitic Rocks. 



III. The Relation between the Uriconian and the Longmyndian 118 



1. The Discordance of Strike between the two Groups. 



(a) LiUesliall Hill. 



(b) The Wrekin Chain. 



(c) The Wrockwardine Mass. 



(d) Charlton Hill. 



(e) The Lawley. 

 (/) Caer Caradoc. 

 (g) Helmeth Hill. 

 (h) Hazier Hill. 

 («■) Ragleth Hill. 



(k) The Cardington and Hope-Bowdler Mass. 



2. The Faulted Junction. 



3. Differences in the Conditions of Deposit. 



I. Introduction. 



About twelve years ago I devoted some attention to the Arehoean 

 rocks of Shropshire, and a communication 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 Archaean 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 



* Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 38G. 

 Q. J. G. S. IS'o. 186. I 



