24(5 SILURIAN OF THE CLUN- FOREST DISTRICT. [vol. lxxiv. 



gradual. The first signs of a change are seen as low down as the 

 Tthynchonella Beds, and they become more pronounced as the 

 sei'ies is ascended. The most important pakeontological change is 

 that at the base of the Temeside Group. With regard to the excep- 

 tional thickness of the Upper Silurian deposits in the Clun-Forest 

 district, there is abundant evidence that the whole deposit 

 accumulated in not very deep water, so that, despite the regional 

 tendency to an uplift due to the oncoming of continental condi- 

 tions, there must also have been local subsidence due to the loading 

 of the sea-floor bj the great weight of sediments. Thus it was 

 possible for a considerable thickness of sediments to accumulate in 

 comparatively-shallow water, in accordance with the theory of 

 isostasy. The sediments were accumulated near a shore-line, 

 where the principal deposition usually takes place, and the rapid 

 eastward thinning of the deposits was probably accounted for by 

 the increased distance from the main land-area whence the clastic 

 material was derived. The outcrop of Old Red Sandstone is so 

 small that it is limited to a thin capping of sandstone on Chin 

 Hill, with the result that the usual red marls are not displayed 

 within the area mapped. The local absence of true ' bone-beds,' 

 both from the Upper Ludlow and from the Temeside Group, sug- 

 gested that (for some reason) fish- remains were not at all common 

 in this particular district, which in this respect certainly displays a 

 striking contrast with the Ludlow area. Lingida cornea occurred 

 abundantly, and was restricted to the Temeside Shales ; whereas 

 L. minima was restricted to the underlying Downton Sandstones and 

 JPlatyscliisma Shales. In conclusion, the speaker wished to con- 

 gratulate the Author on having completed his investigation, despite 

 the difficult conditions under which he had been compelled to work. 



[September 5th, 1919.] 



