Mr. D. Sharpe on the Bala Limestone. 525 



Before entering upon his own views, the author quotes the opinions 

 published by others upon the age of the limestones of Bala and Coni- 

 ston ; previous to the labours of Professor Sedgwick and Mr. Mur- 

 chison, these two calcareous bands were thought to be of the same 

 age, and to be nearly the oldest fossiliferous beds in this country ; 

 but the first definite arrangement of them was made by Professor 

 Sedgwick, whose views will be found in our Proceedings (vol. ii. p. 

 675), placing both these limestones in the Upper Cambrian system, 

 which he stated to lie below the Silurian system of Mr. Murchison, 

 and above the Lower Cambrian system, or old slate series of Car- 

 narvonshire, Cumberland, &c, a view adopted by Mr. Murchison in 

 his work upon the Silurian system, upon the authority of Professor 

 Sedgwick. 



In 1839 Mr. James Marshall classed the Coniston limestone 

 with the Caradoc sandstone, upon the evidence of fossils examined 

 by Mr. J. Sowerby, and pointed out that it rested upon the Lower 

 Cambrian rocks ; thus omitting the Upper Cambrian system in the 

 North of England (Reports of the British Association, vol. viii. p. 67.). 



The second edition of Mr. Greenough's Map adopts Mr. Marshall's 

 view of the age of the Coniston limestone, and omits the Upper 

 Cambrians in the district of the Lakes ; but retains them in North 

 Wales, under the name of Upper division of the lower Killas, in 

 which is included the Bala limestone, thus placed in a different system 

 from the limestone of Coniston. 



Professor Sedgwick's memoir of November 1841 follows the same 

 view (Proceedings, vol. iii. p. 545) ; and in a note, p. 551, that author 

 removes all doubt as to his opinions by apologizing for having for- 

 merly placed the Bala and Coniston limestones on the same parallel. 



Notwithstanding the agreement of our best geologists in placing 

 the Bala limestone in the Upper Cambrian system, Mr. Sharpe was 

 induced to doubt the accuracy of this classification, by observing that 

 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." 



