Vol. 57.] laXEOUS ROCKS OP THE TORTWORXH IXLIER. 271 



parts ainygdaloidal, but much weathered and coutaiaiug a large 

 amount of secondary calcite. 



At one point in the western part of the quarry is a small but 

 instructive exposure, giving the following section. At the top :-— ' 



Inches. 



Red marly shale ■. 4 



Band of grey sandstone f to 1^ 



Red marly shale ;. 8 



Calcareous ash, with lajailli and fossils 9 



Highly amygdaloidal trap, with an exceed- 

 ingly irregular surface 12 (seen). 



The calcareous ash is a well-marked rock, showing in a hand- 

 specimen many fossils, shaly patches, small geodal cavities lined with 

 quartz, and a fair number of characteristic lapilli, the largest being 

 '2 inches long. In a microscopic section it is seen to be a very 

 definite ash, with the following constituents : — 



(a) Small lapilli showing good felspars, and generally much iron-staiiied. 



(6) Felspar-crystals of fair size, some of vrhich still exhibit twinning. 



((?) Quartz-grains. 



(d) Small shaly patches^ 



\e) Fossils, 



These are all cemented together by culcareous matter, and calcite 

 occurs plentifully in veins and patches, some of which are well 

 cleaved. 



Mr. F. E. Cowper Reed, M.A., P.G.S., to whom we wish to express 

 our heartiest thanks for the very great amount of trouble that 

 he has taken in the examination of our fossils, has identified the 

 following forms from the ash-band : — 



Atrypa reticularis, Linn. 

 Spirifera 'plicatella, var. glohosa, Salt. 

 Ehynchospira Bayly i. Da v. 

 Leptcena rhomhoidalis, Wilck. 



Orthis calligramma, Dalm. 

 0. 2^oly gramma (?) Sot^. 

 CyrtocerOjS sp. 



He regards this assemblage of fossils as probably indicative of 

 Wenlock age. In this connection it is interesting to recall that one 

 of us has noted ^ the occurrence of Wenlock Beds in a field south- 

 west of Poolfield Farm. The shale at this spot is crowded with 

 Coenites juniperinus, Eichw., and overlain by a band of limestone. 

 This spot is about 350 yards from Culiimore's Quarry. 



Whether the fossils of the ash-band are of Wenlock age, or occur 

 near the top of the Upper Llandovery Series, there seems little 

 doubt that their association with w^ell-marked lapilli, with felspars, 

 and with other ashy material, afi'ords the strongest possible evidence 

 that there was contemporaneous volcanic activity in Silurian times, 

 and renders it extremely probable that the trap is a contemporaneous 

 lava. With this conclusion the very uneven surface and the highly 

 amygdaloidal character of the trap itself are in agreement. 



The trap is seen again, on about the same horizon, farther south- 

 east, in the garden of a cottage on the south side of the Bibstone 

 road opposite Warner's Court. It is here much shattered, very 

 ^ Brit. Assoc. Excursion-Guide to Tortworth, 1898, p. 11. 



