﻿544 THE rOSSILIEEROTJS SILURIAN ROCKS OF TOETWOETH. [XoV. I908, 



President. He had himself pointed out in his presidential address 

 to Section C of the British Association at Bristol, ten years ago, 

 that, in the great post-Carboniferous uprise of that region, the 

 change from the east-and-west or Armorican axial line, to the 

 north-and-south or Pennine axial line, takes place in the Vale of 

 Berkeley. It was for local geologists to describe the details of 

 these movements, and, if possible, to ascertain the cause. 



The Pellows were much indebted to the Authors for the fresh 

 information now afforded ; and it might be gathered that, on the 

 whole, the Wenlock and Ludlow rocks were much less fossiliferous at 

 Tortworth than in areas farther afield. The presence of celestine 

 clearly pointed to infiltration from above, and it might be that such 

 action had tended to produce alteration in the beds, especially in 

 those of a calcareous nature, which had acted unfavourably as 

 regards the preservation of fossils. 



Dr. C. G. Ctjllis remarked upon the interesting discovery by the 

 Authors of masses of celestine in beds of Silurian age ; but he 

 believed that such masses were not themselves of that age. Much 

 evidence, indeed, pointed to their being of secondary origin. The 

 mineral had never been recorded from Silurian beds of any other 

 part of the country ; it was confined to this particular locality — 

 a locality in which it also occurred in the Carboniferous Limestone, 

 the IVIillstone Grit, and the Keuper ITarl. If it were claimed to be 

 of Silurian age in the Silurian beds, it could equally be claimed to 

 be of Carboniferous age in the Carboniferous Limestone and Millstone 

 Grit, and of Triassic age in the Keuper Marl ; and it seemed very 

 improbable that the peculiar conditions necessary for the deposition 

 of strontium-sulphate persisted continuously, or even intermittently, 

 in the region from Silurian until Triassic times. The celestine 

 was most abundant in the Keuper Marl, which rested horizontally 

 upon the upturned edges of the underlying Palaeozoic rocks, and in 

 this formation there was collateral evidence that the conditions during 

 deposition were precisely those suitable for the precipitation of this 

 and other sulphates. The occurrence of the mineral in various 

 underlying formations could be simply explained by the down- 

 ward percolation along joints and bedding-planes of waters con- 

 taining small quantities of sulphate in solution, and the substitution 

 of this for calcareous carbonate under favourable conditions. 



With regard to the vertical and slightlj^-overtumed structure of 

 the Silurian strata described by the Authors, he referred to the fact 

 that a precisely- similar structure was to be traced northwards across 

 the Severn through the various Silurian exposures, as far at least as 

 the remote end of the Malverns. In the latter region it had always 

 seemed to him that the disturbance might have been caused by the 

 crushing of the older Palaeozoic rocks against a stationary buttress 

 or ' knob ' formed by the pre-Cambrian massif. That massif had a 

 similar north-and-south alignment to that of the upturned or over- 

 turned Silurian beds of the Malverns, May Hill, Newnham, and 

 Tortworth inliers ; and he suggested, as a tentative explanation, 

 that the extreme disturbance along this line might be an expression 



