Trof. T. Sterry Hunt — On Cambrian and Silurian. 391 



upon Sedgwick the responsibility of Murcliison's error. Altliongh 

 the historical sketch, which precedes, clearly shows the real position 

 of Sedgwick in the matter, we may quote farther his own words : 

 " I have often spoken of the great Upper Cambrian group of North 

 Wales as inferior to the Silurian system, .... on the sole authority 

 of the Lower Silurian sections, and the author's many times repeated 

 explanations of them before they were published. So great was my 

 confidence in his work that I received it as perfectly established 

 truth that his order of superposition was unassailable. ... I asserted 

 again and again that the Bala limestone was near the base of the so- 

 called Upper Cambrian group. Murchison asserted and illustrated 

 by sections the unvarying fact that his Llandeilo flag was superior 

 to the Upper Cambrian group. There was no difference between 

 us until his Llandeilo sections were proved to be wrong." (Philos. 

 Mag., IV., vol. viii. p. 506.) That there must be a great mistake either 

 in Sedgwick's or in Murchison's sections was evident, and the Govern- 

 ment surveyors, while sustaining the correctness of those of 

 Sedgwick, have shown the sections of Murchison to have been com- 

 pletely erroneous. 



The first step towards an exposure of the errors of the Siluriaa 

 sections is, however, due to Sedgwick and McCoy. In order better to 

 understand the present aspect of the question, it will be necessary to 

 state in a few words some of the results which have been arrived at 

 by the Grovernment surveyors in their studies of the rocks in ques- 

 tion, as set forth by Eamsay in the Memoirs of the Geological Survey. 

 In the section of the Berwyns, the thin bed of about twenty feet of 

 Bala limestone which (as originally described by Sedgwick) they 

 have found outcropping on both sides of the synclinal chain, is 

 shown to be intercalated in a vast thickness of Caradoc rocks ; 

 being overlaid by about 3,300 and underlaid by 4,500 feet of strata 

 belonging to this formation. Beneath these are 4,500 feet additional 

 of beds described as Llandeilo, which rests unconformably upon the 

 Lingula-flags just to the west of Bala ; thus making a thickness of 

 over 12,000 feet of strata belonging to the Bala group of Sedgwick. 

 A small portion of rocks referred to the Wenlock formation occupies 

 the synclinal above mentioned. (Memoirs, vol. iii. part 2, pp. 214, 222.) 

 The second member, in ascending order, of the Silurian system, to 

 which the name of Caradoc was given by him in 1839, was originally 

 described by Murchison under the names of the Horderley and May 

 Hill sandstone. The higher portions of the Caradoc were subse- 

 quently distinguished by the Government surveyors as the Lower 

 and Upper Llandovery rocks ; the latter (constituting the May Hill 

 sandstone, and known- also as the Pejziamerws-beds) being by them 

 regarded as the summit of the Caradoc formation. In 1852-, however, 

 Sedgwick and McCoy showed from its fauna that the May Hill sand- 

 stone belongs rather to the overlying Wenlock than to the Caradoc 

 formation, and marks a distinct pala3ontological horizon. 



This discovery led the geological surveyors to re-examine the 

 Silurian sections, when it was found by Aveline that there exists in 

 Shropshire a complete and visible want of conformity between the 

 underlying formations and the May Hill sandstone ; the latter in 



