CAMBRIAN ROCKS IN SHROPSHIRE — THE LONGMYND, ETC. 



257 



Let us first consider the structure of the Longmynd or principal mountain of this 

 group 1 . 



The stratified rocks of the Longmynd are sandstones, grits, schists, and imperfect 

 slates, of grey and purple colours, in which no traces of organic remains have been de- 

 tected. Although the outlines of these hills are round and waving, like those of most 

 slaty tracts, the strata are admirably exposed in a number of deep transverse ravines, or 

 as they are here termed " gutters 2 ," on ascending any of which the various strata are 

 seen on their sides. 



On the eastern flank of the Longmynd or western side of the valley of Church Stretton, we first 

 meet with a zone of black and dark-coloured clay slate of fine texture. This rock is so shattered 

 and splits under the hammer into such cubical fragments that it is with difficulty a fresh fracture 

 is obtained. It is generally very glossy on the surface, very finely laminated, and traversed by a few 

 veins of white quartz and carbonate of lime. It is thrown about at very high angles of inclination, 

 being penetrated by numerous bosses of greenstone, which will be spoken of hereafter. The 

 succession of strata to the west of this clay slate, can be well studied in any of the transverse in- 

 dentations which diversify the outline of these hills, trending in parallel lines at right angles to the 

 strike. The following account may be taken as a general description of the order in which the 

 strata are exhibited, in crossing their edges from south- south-east to north-north- west. 



1. Black clay slate. 



2. Greenish compact slate passing into hard, greenish grey, micaceous, slaty sandstone, which breaks into cubical frag- 

 ments, in beds of two to four inches thick, veined with white quartz. 



(Excellent examples of these beds are seen near the mouth of the carding-mill gutter above Church Stretton.) 



3. Deep purple-coloured, compact slate, alternating with lightish green, hard, micaceous sandstone. This purple-co- 

 loured slate becomes from this point the predominant rock. It is very fine-grained and rarely micaceous. 



4. Bluish gray, slaty, micaceous sandstone, alternating with the purple slate. 



5. Dull, greenish clay slate passing into a compact rock, approaching to hornstone. There are countless alternations of 

 these beds, and a vast thickness of strata is exposed before we reach the higher grounds where the slates and slaty sand- 

 stones pass into 



6. Purple-coloured grits and sandstone with nests of crystals of quartz and quartz veins. 



7. Thick-bedded, quartzose conglomerates with a base of red and purple sandstone, containing disseminated mica, with 

 fragments and pebbles of grey and white quartz, varying in size from pins-heads to walnuts : some of the pebbles contain 

 cavities filled with chlorite. In other instances they have the appearance of having been altered by heat and indented 

 against each other. 



These conglomerates and purple-coloured sandstones constitute the central masses of the Long- 

 mynd, and are succeeded on the west by alternations of similar strata (Prolimoor and Wentnor.). 

 They are again followed upon the north-west by various alternations of strata identical with those 

 described, and of which most of the beds of the rivulets between the crest of the ridge and Ratling- 



1 Most of the Cambrian rocks have a mountain character. The summits of the Longmynd, for example, are 

 covered with heath and tenanted by the red or common grouse. Although it is generally considered that there 

 is no road across these hills, the venerable Earl of Powis, to whom a large portion of the tract belongs, 

 accompanied by Dr. Du Gard, recently passed over them in his carriage, and descended into the valley of 

 Church Stretton by the narrow track represented in the foreground of the sketch, p. 255. 



2 Probably so called from the feeble rivulets which flow in them. 



