Geological Society. 225 



Fourthly, Although the loess when pure appears unstratified, it 

 must have been formed gradually, as the shells contained in it are 

 numerous and almost all entire, and beds of shelly loess sometimes 

 alternate with strata of gravel or volcanic matter. 



Fifthly, Some volcanic eruptions must have taken place during 

 and after the deposition of loess. 



In conclusion, the author states that great changes must have oc- 

 curred in the physical geography of the basin of the Rhine since 

 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. — 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 stratified Deposits," by Roderick Impey Murchison, Esq., 

 V.P.G.S. F.R.S. &c. 



Having established an order of succession in the various sedimen- 

 tary formations between the carboniferous series and the older 

 grauwacke slates, the author 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 previously noticed. 



These rocks mark parallel axes of different lengths on the north 

 bank of the Severn, 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 



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



+ See the "Table of the stratified Deposits,"&c.,in our last voUime,p. 370. 



Third Series. Vol. 5. No. 27. Sept. 1834. 2 G 



