85 



some of the loess was deposited, and consequently at a comparatively 

 modern geological era, when the recent testacea existed. 



As the waters must have been at rest when the loamy sediment 

 was thrown down, we must suppose one or many temporary lakes 

 and ancient barriers which have since been removed. It is shown 

 that to assign the probable places of these would be very difficult, 

 and more data are required respecting the greatest height which the 

 loess attains. 



May 21. — Thomas Clements Pan% Esq., was elected a Fellow of 

 this Society. 



A paper was read, " On certain Trap Rocks in the Counties 

 of Salop, Montgomery, Radnor, Brecon, Caermarthen, Hereford, 

 and Worcester; and the Effects produced by them upon the strati- 

 fied Deposits," by Roderick Impey Murchison, Esq., V.P.G.S. 

 F.R.S. &c. 



Having established an orderof succession in the various sedimen- 

 tary formations between the carboniferous series and the older 

 grauvvacke slates, the autlior proceeds in this memoir to explain 

 the nature of the trap rocks which rise to the surface in the region 

 under review. These rocks are described in the following order, 



1st. Those which protrude in separate ridges through various 

 members of the grauwacke series between Lilleshall Hill, Salop, on 

 the north-east, and Llangadock, Caermarthenshire, on the south- 

 west. 



2nd. The Malvern and Abberly Hills, including dykes which tra- 

 verse the old red sandstone. 



3rd. Rocks penetrating the coal measures. 



I. Shropshire and Montgomeryshire. — Lilleshall Hill consists 

 chiefly of compact felspar rock, having in parts a sienitic structure. 

 The Wrekin, which has been described by Mr, A. Aikin in the 

 Geological Transactions*, is of nearly similar composition. Lea and 

 other rocks near Wrockardine have the same base, but pass into 

 porphyry and clinkstone. 



In Charlton Hill, porphyries and greenstones occur where they 

 had not been pi'eviously noticed. 



These rocks mark parallel axes of different lengths on the north 

 bank of the Sevei'n, ranging from north-east to south-west, and 

 piercing through beds of grauwacke, chiefly those of the third, or 

 Horderley and May Hillf formation, the sandstones of which, on 

 the sides of the Wrekin and Arcal, and at Charlton Hill, are con- 

 verted into quartz rocks at their points of contact with the trap. 



The line of disturbance occasioned by the protrusion of the zone 

 of Charlton Hill, is traced in certain trap rocks which appear in the 

 bed of the Severn, near Cound, extending thence to the south-west. 



Caer Caradoc. — This remarkable ridge, formerly described by 

 Mr. A. Aikin :{:, is on a line of eruption parallel to that of the Wrekin. 



* Geol. Trans., 1st Series, vol. i. p. 191. 



t Ante, Table, p. 13, 



X Geol. Trans., 1st Series, vol. i, p. 207- 



