11 



everyone admitted that the Bala fossils agreed, as far as they had 

 been examined, with those of the Lower Silurian beds, and that there 

 was no clear line of separation between the Lower Silurian and Up- 

 per Cambrian groups : but his attention was particularly drawn to 

 this district by Mr. Bowman's, observations on Denbighshire, laid 

 before the British Association in 1840 and 1841, and since published 

 in the first volume of the Transactions of the Geological Society of 

 Manchester, p. 194, which Mr. Sharpe regards as the first indication 

 of the true structure of this part of North Wales ; Mr. Bowman 

 classes as Upper and Lower Silurian many beds before mapped as 

 Upper Cambrian, showing that the previous classification of the rocks 

 of North Wales could not be relied upon. 



Mr. Sharpe quotes largely from Mr. Murchison's Address from 

 the Chair in February 1842, to show that the Upper Cambrian can- 

 not be separated from the Lower Silurian beds by the help of organic 

 remains, as " Lower Silurian species range through the Upper Cam- 

 brian rocks, and throughout the whole of North Wales," and " pre- 

 vailed during that vast succession of time which was occupied in the 

 accumulation of all the older slaty rocks previous to the Upper Silu- 

 rian period." 



Mr. Sharpe points out, that up to the moment of his taking up the 

 subject no one of the authors quoted had expressed a doubt of the 

 existence of a great thickness of fossiliferous beds below the Caradoc 

 sandstone and Llandeilo flags, although it was admitted that these 

 supposed beds could not be distinguished by their fossils from the 

 Lower Silurian ; and he states that the object of his communication 

 is to show the error of this view as relates to the Bala rocks, 

 which he proposes to prove to be the equivalent of the Lower 

 Silurian beds described by Mr. Murchison, and not part of an older 

 series ; and he infers from^analogy that the same will be found to be 

 the case in other parts of North Wales which he has not visited, where 

 he conjectures that all the rocks containing shells of Lower Silurian 

 species will also prove equivalents of the Lower Silurian beds. In- 

 stead of continuing the Silurian system downwards through a vast 

 thickness of slate rocks, Mr. Sharpe proposes to strike out one of its 

 oi'iginal members, regarding the Caradoc sandstone and Llandeilo 

 flags as one and the same formation which has received different 

 names according to its mineral character ; he observes, in confirma- 

 tion of this view, that both formations are never equally developed 

 in the same district, and that the fossils found throughout are too 

 nearly the same to warrant the separation of the lower beds under a 

 separate name. Still Mr, Sharpe believes that there are in Wales, 

 as in Westmoreland and Cumberland, vast accumulations of slaty 

 rocks below the Silurian system, in which no fossils have been found, 

 and which must retain the appropriate name of Cambrian rocks. 



Mr. Sharpe did not map the district in detail, but he traced two 

 sections to show the position of the Bala beds with regard to the 

 Berwyns, as he considered the question to turn upon the accuracy 

 or error of the statement of Mr. Murchison, p. 308, " that the Bala 

 limestone dips under the chief mass of the Berwyns." 



