166 Br. Wheelton Hind — The Yoredale Series. 



The Geological Survey has considered the uppermost member of 

 this series to be the equivalent of the Millstone Grit, because 

 it passes into a pebbly sandstone further south. Mr. Morton has 

 shown that at Pentre Halkin the white shale interstratified 

 with the chert beds contains Chonetes Laguessiana and Productiis 

 longispinus. Several other typical Lower Carboniferous species 

 are stated to be found in these so-called Millstone Grit beds, 

 on the authority of the Survey ; but 1 am bound to admit that 

 Aviculopecten fainjraceus and Posidonomya Gibsoni, whatever may 

 be meant by this last name, are credited the former to one and the 

 latter to two localities, undetermined Goniatites also occurring with 

 the former. 



Mr. Morton observes (Trans. Manch. Geol. Soc, vol. xvii, p. 81, 

 18B3) : " As the fossils found in the Cefn y Fedw sandstone are all 

 common limestone species that occur in Denbighshire and Flintshire, 

 it seems possihle that the formation is an arenaceous continuation of 

 the Carboniferous Limestone." 



At Saith-aelwyd the chert beds are immediately above the Black 

 Limestone. The section of the chert beds at Afongoch^ gives — 



feet. 



Banded chert 6-8 



Chert full of encrinites ... ... ... ... ... 3 



Chert and limestone — sometimes all crystalline limestone, 

 sometimes containing blocks oi chert with a heart of 



limestone, or vice versa ... ... ... 1 



Banded chert 8 



It is definitely demonstrated that the chert has either replaced 

 limestone or was deposited at the same time. It is very questionable, 

 therefore, whether strictly any equivalents of the Millstone Grit occur 

 in North Wales. It must be remembered also that, although sand- 

 stones of various degrees of coarseness are known in the Lower 

 Carboniferous Series, chert beds are conspicuously absent in the 

 Millstone Grit Series of Lancashire and Derbyshire. 



I have been impressed with the occurrence of beds of stratified 

 chert in the Upper Yoredale Series of Wensleydale, and the fact that 

 similar beds occur in the upper portion of the Carboniferous 

 Limestone of Derbyshire ; and, although I would hesitate to say 

 that this occurrence of beds of similar chemical characters in the 

 upper beds of the two series is any positive evidence as to these 

 bfds being either the chronological or homotaxial equivalents of 

 each other, I give the fact for what it is worth as indicating one 

 other feature which the massif of Carbon ifei'ous Limestone and the 

 Yoredale beds of North Yorkshire have in common. 



I have written elsewhere (Geological Magazine, Dec. IV, 

 Vol. Ill, p. 259) : — "The Carboniferous series of Northumberland 

 and Scotland are essentially characteristic of those [beds] deposited 

 near a shore which occasionally became land, and occasionally was 

 depressed deep enough to allow limestones to accumulate on its 

 floor. The land which was the source of the muds and sandstones 

 was probably of no great elevation, and consequently river-action 

 1 Mem. Geol. Surv., " Geol. Flint, Mold, and Euthin," p. 48. 



