﻿590 DE. T. GEOO:iI AisD MK. P. LAKE OS THE [XoV. I908, 



Man & Eoberts placed the Eobeston-Watheii Limestone in the 

 Middle Bala and the Sholeshook Limestone in the Upper Bala, 

 but they expressed themselves with some reserve. In the presence 

 of Halysites, Heliolites, and other corals, the Robeston-Wathen 

 Limestone resembles the Dolhir Beds ; but it differs in the absence 

 or rarity of cystideans and polyzoa, and of Cylele, Cheirurus 

 juvenis, Trinudeus seticornis. and other trilobites. It contains, 

 however, none of the characteristic fossils of the Pandy Beds ; and in 

 the Glyn-Ceiriog district it must be represented, either by a part 

 of the Dolhir Series, or by a part of the succession that is cut out 

 by the Dolhir Fault. In either case, it is clear that the Uobeston- 

 Wathen Limestone belongs to a higher horizon than the Pandy Series. 



TVhatever uncertainty may exist as to the correlation of the 

 D{crcmog?^a2)tus-Sh.ales and the Bobeston-AYathen Limestone, there 

 can be no doubt that the succeeding beds are approximately the 

 equivalents of the Dolhir Series. In both we have the same 

 abundance of corals, cystideans, and polyzoa ; in both Cyhele 

 verrucosa^ Trhmcleus seticornis, Cheirurus juvenis, Ch. octolobatus, 

 and Remopleurides are characteristic among the trilobites. The 

 most important difference is the absence in the Dolhir Beds 

 of Phillipsinella parabola and Staurocephalus, both of which are 

 common in the Sholeshook Limestone. 



The Eedhill and Slade Beds do not differ essentially in fauna 

 from the Sholeshook Limestone, although they seem to be less 

 fossiliferous and to contain fewer species of trilobites. The lime- 

 stone passes upwards into the Eedhill stage, and no sharp line 

 can be drawn between the latter and the Slade Beds. The three 

 divisions appear to form a single natural group, and that group is 

 characterized by a fauna similar to that of the Dolhir Series. 



Since in South Wales the base of the Bala Series lies in the 

 Blcranegraptus-^halea, and in Xorth Wales below the Pandy Beds, 

 and since the Eobeston-Wathen Limestone of South AY ales belong,:5 

 to a higher horizon than the Pandy Beds of jS'orth Wales, we are 

 forced to conclude either that the Pandy Beds are represented by 

 the upper part of the Dicranograptus-^hales, or that in South 

 Wales they are altogether absent. In the latter case there must 

 be a break in the succession below the Eobeston-A\'athen Lime- 

 stone. Until, however, we know to what horizon the Dicrano- 

 ^rap^i*s-Shales extend there can be no certainty on this point. 



The Bala or Coniston-Limestone Series of the Lake District 

 was divided by Dr. Marr in 1S92 ^ into the following groups, in 

 descending order : — 



III 5. AshgiU Shales. 



Ill a. Staurocephalus-JAmesXone. 



II. Sleddale Group. 



I. Rouiau-Fell Group. 



At that time he included the Keisley Limestone in the Sleddale 

 ^ Geol. Mag. dec. 3, vol. ix (1892) pp. 97-110. 



