410 



Dr. G. L. Elles— 



distinct, though both occur in the same heels. I have also given reasons 

 for the suggestion that on the evidence available, admittedly not 

 entirely satisfactory, the beds in question were more likely to be of 

 Silurian than of Ordovician age. This summer I have obtained 

 additional evidence which goes considerably further towards the 

 solution of the problem. 



[ - . '. \ Moelfryn Sand- 

 stones. 



Phacops Mud- 

 stones. 



/Am Hirnant Beds. 



Valentian. 



Fig. 1. — Sketch-map of Bwlch yr Hwcli. Scale 6 inches = 1 mile. 



Close to Bwlch yr Hwch (Fig. 1), in the Hirnant Valley, where 

 these Hirnant Beds are typically developed, they consist of a series 

 of soft blue-grey mudstones, some of which are calcareous, containing 

 the well-known pisolitic Hirnant Limestone in large concretionary 

 masses ; these beds have yielded : — ■ 



Orthis hirnantensis M'Coy. C. Strojjhomena siluriana Dav. C. 



Orthis sagittifera Dav. C. Plattjstrophia biforata var. 



fissicostata (Schloth.). 

 Dalmanella elegantula (Dalm.) Monticulipora fibrosa (M'Coy.). 



This is the characteristic " Hirnant " fauna. 



