LONGMYIS'D AND AECHiEAN ROCKS OF SHROPSHIEE. 485 



glomerate does not indeed prove that all the altered rocks of Ireland 

 and the Highlands are Archaean ; but the evidence it furnishes 

 deserves consideration. 



It will be seen from the following note, which the writer kindly 

 permits me to publish, that Prof. Bonney is in substantial accord 

 with my identification of the fragments in the conglomerate and 

 with the inferences based upon them : — 



'^ Your slides confirm the anticipation raised by my own specimens 

 of the Charlton conglomerate, that it would be found to contain 

 fragments of schists of a newer type than we might expect to find 

 among the typical Malvernian rocks. Coarse granitoid rocks, some- 

 times consisting mainly of quartz and felspar, sometimes containing 

 a fair amount of green minerals probably replacing hornblende or 

 augite, are common. These may in some cases be true igneous rocks, 

 but others exhibit structures allied to the gneisses — in short, they 

 oifer the same difficulties that we generally find among the roekt^ 

 which, when we can settle their stratigraphical position, we know 

 to be of great antiquity. The fragments are such as we should expect 

 to obtain from rocks similar to those exposed at either end of the 

 Wrekin and in the Malvern chain. But besides these there are 

 schists, quartzose and micaceous, which remind me of those which 

 occur at higher horizons in Scotland and in Anglesey, and in the 

 uppermost group of the true schists in the Alps. In addition to 

 these we have quartzites and grits, exhibiting a certain amount of 

 metamorphism, also an argillite, and varieties of rhyolitic rocks, 

 suggestive of a volcanic origin." 



Discussiois-. 



The President remarked on the difficulty, as a general rule, of 

 identifying pebbles in a conglomerate bed, though there are doubt- 

 less some rocks of such striking characteristics that identifications of 

 this kind may be made with a high degree of probability. 



Professor Hughes quite agreed with the Author that there was 

 abundant evidence from the masses of Archaean now seen in that 

 district that the rocks exposed there in Pre-Cambrian times con- 

 sisted of granitoid rocks, felstones, and various schists. He had 

 himself found pebbles of granitoid rock in the conglomerate of 

 Charlton Hill ; but he thought that the Charlton-Hill conglomerate 

 was the base of the Cambrian, and could not understand the Author's 

 argument if he called it Archaean. 



Prof. Bonney said that the most characteristic varieties of the 

 Lea rock had not been and were not likely to be found, but rocks 

 similar to the devitrified pitchstones of the district were abundant. 

 He was under the impression that the Charlton-Hill conglomerate 

 was Pre-Cambrian, at least that it was older than the quarizitCy 

 and was not immediately connected with the volcanic rocks of 

 the Wrekin. The speaker explained Dr. Callaway's views, and 

 showed the resemblance of the fragments found in the Charlton-Hill 

 conglomerates to rocks occurring in the Malvern series and some of 

 the Archaean rocks occurring in the Alps and elsewhere. 



Q.J.G.S, No. 168. 2l 



