546 EEV. J. F. BLAKE OX THE 



brian, and it is not Archaean, but it is the basis and foundation, so far 

 as we have yet discovered, of all our systems of stratified rocks on 

 this side of the Atlantic. 



EXPLANATION OF PLATE XIII. 



Fig. 1. Map of the distribution of the rocks of the Monian System and 

 associated rocks in the island of Anglesey. (Scale ^ in, to 1 mile.) 



Fig. 2. Map of the distribution of the rocks of the Monian System and 

 associated rocks in the Lleyn Peninsula. (Scale f in. to 1 mile.) 



Discussion. 



The Peesidext spoke of the interest attaching to this paper, and 

 the vastness of the subject. He thought, however, that a new 

 system should be proved over a larger area than Anglesey. If the 

 Author's system is a real entity it will be found elsewhere in 

 Europe. 



Dr. Hicks thought that the Author had by no means evolved 

 order out of chaos. If there was anything in Anglesey worth 

 naming, it would be found at St. David's and elsewhere. He regarded 

 his own three series, for purposes of correlation, as of equal value. 

 There was hardly a rock in Anglesey which he had not found in 

 Caernarvonshire, either in situ, or in the Cambrian conglomerates. 

 He denied the Author's right to speak of all the beds above the 

 conglomerate as Ordovician ; he considered the conglomerate to be 

 Pre-Ordovician ; there was a great series under the Tremadocs in 

 that very area. So far from no names having been suggested, he 

 had called one group the Holyhead Series, another the Menai Series : 

 the main portion of the Pebidian was still newer. Dealing with 

 the question of the granitoid rocks, these, he believed, were originally 

 of igneous origin, but pebbles derived from such rocks were found 

 in beds very much older than the Tremadocs. The Anglesey granite 

 was unlike the Killiney granite, but resembled the Pre-Cambrian 

 granitoid rocks of St. David's, the Lleyn, and Caernarvon. After 

 referring to the character of Arvonian and Pebidian rocks, and 

 more especially to their discovery as rolled pebbles in the neigh- 

 bouring conglomerates, he said that the greatest disagreement was 

 as to the central granite-boss. He had always maintained that 

 it did not protrude and alter the Silurian or Cambrian rocks : he had 

 shown that it was Pre-Cambrian, as proved by its derivatives. He 

 considered that the evidence of intrusion even into the older rocks 

 adduced by the Author was fallacious. He believed the granite to 

 be one of the oldest rocks in Anglesey, and to have been much 

 crushed and changed in Pre-Cambrian times. He was more disposed 

 to regard the diorite as intrusive into the granite. 



Prof. Hfll was sure that the Author had left no stone unturned 

 in order to arrive at his conclusions. Some six years ago he had 

 accompanied Sir A. Eamsay over the district of the Menai Straits, 

 and the latter concluded that he had not been mistaken in his 



