262 THE EOCKS MAPPED AS CA31BilIAN IJf CAERNARVONSHIRE. 



and that since then some of the zones had been worked out with 

 much success. In his recent memoir on the OleneUus-iaun?^, 

 Mr. Walcott says that the Coiwcory phe-viola zone above the Penrhyn 

 quarry must be included in the Lowest Cambrian ; therefore it is 

 clear that the lowest beds of the Cambrian occur in the succession 

 on the east side of the quartz-felsite axis. The conglomerate which 

 rests on this axis and underlies the beds which contain the earliest 

 known Cambrian fauna must be considered to mark the base-line of 

 the Cambrian in this area. 



Mr. Maer thought that the distribution of the conglomerate seen 

 at Llanberis and on Moel Tryfaen was difficult to account for if the 

 rock was post-Cambrian. He had noticed blocks of a breccia resem- 

 bling the conglomerate on the summit of Moel Tryfaen amongst the 

 talus thrown out at the mouth of the adit on the hillside. 



Prof. Blake replied that something that might be called a con- 

 glomerate often followed the felsite anywhere ; but where he had 

 drawn the latter as intrusive, the stratigraphical evidence seemed to 

 point to its being so, whatever the ' purple slate ' might be. As 

 to the Para(h.vides, &c., they could be discussed when they had 

 been seen. His conclusions depended very much upon details of 

 mapping, and the criticisms of those who were not acquainted with 

 these details were apt to be somewhat wide of the mark, but he 

 believed that some truth would be found in his paper. 



