168 DR. a. L. ELLES 01^ THE BALA COUNTET : [vol. Ixxviii, 



p. 172). Phillipsinella parahola appears to be both generically 

 and specifically a characteristic Ashgillian form, although many 

 other trilobites more characteristic of the fauna have a much 

 longer range in time. Here it may be noted that the general 

 faunal lists of the beds belonging to this horizon are often rather 

 misleading, for the}'" do not bring out the degree of resemblance 

 that undoubtedl}^ exists, since species are apt to be different in 

 widely separated areas and thus the strong generic resemblance is 

 often obscured. The essential distinction between the Caradocian 

 xind the Ashgillian faunas as found over the greater part of Wales 

 and the Lake District lies in the genera rather than in the 

 species of trilobites ; the species, however, are all-important in 

 discriminating between the Ashgillian fauna proper and the earl}'- 

 faunas of Ashgillian type, although indeed some forms are common 

 throughout. 



Thus, two widely- separated areas, both containing abundant 

 Phillipsinella parabola, and therefore presumably of Ashgillian 

 age, may yield many Cheirurids, Lichads, and Reraopleurids, and 

 yet have no species of these genera in common. Consequently, 

 the attempt to show the relationshiiD that probably exists between 

 the faunas of the Rhiwlas Limestone and Mudstones and those 

 of the Phillipsinella Beds of the Cautley area, the area west of 

 Coniston Lake, the Keighley Limestone, the Chair-of-Kildare 

 Limestone, and the Sholeshook Limestone in South Wales cannot 

 be regarded as satisfactory (p. 172) : there is, in reality, a greater 

 resemblance than these lists indicate. 



The Foel-y-Ddinas Beds of Bala represent part, at any rate, of 

 Marr's Phacops-mucronatus Beds, although the fauna is very 

 meagrely represented (see p. 156). Marr's Ashgill Shales, on the 

 other hand, contain a fauna which recalls strikingl}^ that of the 

 Hirnant Beds, and, if the two belong really to the same horizon, the 

 question of the upper limit of the Ashgillian Series seems to be 

 involved. The section as seen at Cwm-Hirnant is, in my opinion, 

 strongly suggestive of the Lower Llandovery age of the Hirnant 

 Beds, as otherwise the whole of the Llandovery Series inust be 

 comprised within 150 feet of rock — not impossible in an area of 

 deep-water deposition, but hardly likely in a district where shallow- 

 water deposits occur so abundantly in such close proximity. 



The sections at Conway ^ would confirm this view. 



In conclusion, I would offer my grateful thanks to the many 

 members (past and present) of the Cambridge University Sedgwick 

 Club, who have helped me during the progress of this work, more 

 particularly my pupils Miss H. Drew, Miss A. B. Dale, Miss 

 E. W. G-ardner, Mrs. J. Eomanes, and Miss M. E. J. Chandler, 

 and Mr. W. B. E. King and Mr. T. C. Nicholas. 



To Prof. Marr I am much indebted for consultation in matters 

 relating to the Ashgillian as a whole, and for permitting me to 

 refer to his collections from the Lake District. 



1 G. L. EUes, Q. J. G. S. vol. Ixv (1909) p. 169. 



