420 MONIAX AND BASAL CAMBRIAN KOCKS Oi*' SHROPSHIRE. 



main, his owu views were much more iu accord with those of 

 Dr. Callaway than with those of the Author, lie failed to see any 

 reason why the Author should call any of the Longmynd rocks 

 (which already had local names given to them) by the name 

 '' Moniau," especially since they were entirely unlike the rocks in 

 Anglesey, which the Author had recently called by that name. 

 Dr. Hicks had examined most of the sections, referred to by the 

 Author, last autumn. He believed the Longmynd rocks to be 

 mainly Cambrian, and the two series to represent the Caerfai 

 and Solva groups of St. Davids, which contained similar fossils to 

 those of the Longmynd rocks. Between the Caerfai and Solva 

 groups there were Av^ell-marked grits and conglomerates. The 

 materials composing the Lower Longmj^nd series had undoubtedly 

 been derived by denudation from volcanic rocks, such as those now 

 forming the Pre-Cambrian rocks of Caer Caradoc, hence the Long- 

 mynd rocks were clearly newer than the Uriconian (Pebidian) rocks 

 of the area. The sections, on careful examination, showed that the 

 Lower Longmynd rocks had formed an arch over the Caer Caradoc 

 rocks, that the limb on the west side had been greatly broken by 

 reversed faults, and that the limb on the east had been broken by 

 great thrusts which had caused newer beds to be pushed over and 

 hide the older. The Author, Dr. Hicks believed, had here, as he 

 had done at iSt. Davids and in Caernarvonshire, entirely failed to 

 realize the true interpretation by overlooking the effects due to 

 thrusts and faults. In those areas he had also attributed contact- 

 changes to Pre-Cambrian rocks, when entirely due to dykes which 

 penetrated the Pre-Cambrian and overlying series. There was no 

 evidence to show that the Bray Head rocks were of the same age as 

 the Pre-Cambrian rocks of Anglesey. 



Mr. Whitaker asked whether the Author's results were in 

 accordance with those of Prof. Lapworth. 



Mr. Marr objected to the use of the term Monian for a system 

 whose upper and lower limits were not defined. He pointed out 

 the discrepancy between the supposed basal Cambrians on either side 

 of the ridge. 



The Author replied that the Bray Head rocks followed naturally 

 upon the Howth Head rocks which were continued into Anglesey. 

 The statement that the purple slates were derived from older acid 

 rocks might be equally true of any other slates, and did not prove 

 that they were derived from any definite volcanic series. He had 

 seen no evidence for any of the thrusts imagined by Dr. Hicks 

 nor had he seen anj^ of the dykes. He admitted that the summit 

 and base of the system were not defined, but the system itself was 

 there. The beds below the Shineton Shales on the west side were 

 continuous to the base of the Cambrian. 



