Second Precambrian Group in the Malvern Hills. 65 



23,000 feet; and the fossils are found in the upper beds only. 

 Instead of occupying only about 12 square miles, as shown on the 

 Survey Maps, they extend over nearly 200 square miles, and reach 

 southward beyond the Helford Paver, and westward to Marazion. 

 The strike of these rocks is from north-east to south-west. 



4. Tlit Ponsanooth Beds occur beneath the Lower Silurians, and 

 unconformable with them (strike north-west to south-east): they 

 are often crystalline, and are estimated at 10,000 feet thickness. 



Each of these formations has its own set of intrusive rocks : each 

 has been contorted and in part denuded away before the deposition 

 of its successor. 



The various granitic bosses have been pushed through this already 

 complex mass of stratified rocks without materially altering their 

 strike, which does not in general coincide with the Hue of junction. 



The chemical effects of the igneous intrusions are generally con- 

 siderable, and somewhat proportioned to their relative bulk. 



3. ;; On a Second Precambrian Group in the Malvern Hills."' By 

 C. Callaway. Esq.. D.Sc. F.G.S. 



These rocks occupy an area of about half a square mile on the 

 east of the Herefordshire Beacon: they are compact, flinty ••horn- 

 stones.'' very like some of the rocks at Lilieshall, in Shropshire, 

 which belong to the newer Precambrian group of the TVrekin. The 

 strike is not distinct, but probably is quite discordant from that of 

 the subjacent gneissic rocks. As in Shropshire, so here Hollybush 

 sandstone and Dietyonema-shalee occur on the flank of the Precam- 

 brian mass, and each seems to have formed an island in the Lower- 

 Silurian seas, which, during the formation of the May-Hill group, 

 was depressed. In fact, in both regions the chief movements of 

 upheaval, subsidence, and dislocation appear to have been contem- 

 poraneous. Thus they are very probably of the same age; and this 

 probably is that of the Pebidians of St. David's, to some of which 

 they have, lithologically, a very close resemblance. 



June 9, 1880.— Bobert Etheridge, Esq., F.E.S., 

 President, in the Chair. 



The following communications were read : — 



1. " On the Occurrence of Marine Shells of existing Species 

 at different Heights above the present Level of the Sea.'" By J. 

 Gwyn Jeffreys. LL.D.. E.B.S., Treas. G.S. 



This paper resulted from the author's examination of the Mollusca 

 procured during the expeditions of H.M.SS. ' Lightning ' and ; Por- 

 cupine'* in the "North. Atlantic. He stated that he found several 

 species of shells living only at depths of not less than between 

 1 and 10,000 feet, which species occurred in a fossil state in 

 Calabria and Sicily at heights of more than 20Q0 feet, such depths 

 and heights together exceeding the height of Mount Etna above 



Phil Mag. S. 5. Vol. 10. No. b ( X July 1880. F 



