258 



CAMBRIAN ROCKS IN SHROPSHIRE— THE LONGMYND, ETC. 



hope afford instructive sections. Still further to the west the purple-coloured grits, sandstones, and 

 slaty schists again prevail, occupying all the hills extending from Linley to Pulverbatch. The red 

 grits (the compound sandstone of Dr. Townson) are evidently of regenerated origin, and often 

 contain many small fragments of older slate in a quartzose cement. 



Besides these deposits of obvious mechanical origin, there are in the Longmynd, interpolated 

 strata of slaty felspar rock. These are sometimes so compact as to amount to hornstone ; in other 

 cases they are somewhat porphyritic, with flakes of green earth parallel to the lamination. Such 

 rocks might more properly speaking be treated of hereafter among the trap rocks, but it seems 

 impossible to avoid mentioning them, since they are conformably interlaminated with the sandstone 

 and slates. There are, however, also other trappean rocks chiefly greenstone and compact felspar 

 rocks, which as they jut through the inclined edges of the strata in irregular bosses, and exhibit, 

 all the marks of having been intruded, will be presently described. (PI. 32. f. 1.) I have said that 

 on the whole, these ancient stratified rocks have more of the slaty cleavage than any of the over- 

 lying deposits. The cleavage planes nevertheless, though marked upon the great scale, are not 

 always clear, consisting rather of a number of minute foliations, which collectively impress upon 

 the rock an ill-defined cleavage. In some of the combs towards the south-eastern end of the 

 Longmynd, there are excellent opportunities to clear up any obscurity respecting the true stratifi- 

 cation of the mountain, for we there see lines of true cleavage, and also of joints, traversing 

 the various stratified layers, of entirely dissimilar mineral characters. The line of deposition of 

 these beds is clearly marked by the ends of these stratified masses, each composed of different 

 materials, being exposed on the opposite sides of the " gutters" or combs. It will be shown 

 hereafter, that in this district these great masses of slaty greywacke have undergone powerful 

 movements of elevation anterior to the deposition of the Caradoc sandstones, the two systems 

 being placed in marked unconformability to each other, thus explaining the course of that great 

 break or interval to which allusion has already been made. (PI. 33. f. 1. and PI. 32. f. 4.) 



The rocks which extend in the narrow ridge from Pulverbatch to Lyth, and Sharpstone Hills, 

 and reappear at Haughmond Hill, near Shrewsbury, are composed of one or more of the strata 

 above described, associated as in the Longmynd and Linley Hills with trap rocks. 



Trap, altered rocks and veinstones of the upper group of the Cambrian System as seen in 

 the Longmynd and lAnley Hills, and their points of prolongation in Pont esf or d, Lyth, 

 and Haughmond Hills. 



Having stated that the chain of verdant and round-topped hills called the Longmynd, 

 rises to a height of 1600 feet above the sea, that its major axis is nearly parallel to 

 the Caer Caradoc, and that it is chiefly composed of certain slaty rocks and conglome- 

 rates of the Cambrian system ; I proceed to describe the trap and altered rocks with 

 mineral veins which are associated with these old deposits. 



Commencing with the valley of Stretton, we no sooner descend from the flanks of the Caradoc 

 and approach the sides of the Longmynd, than we meet with several outbursts of crystalline green- 

 stone, which cut through the black schist above described. One of the chief masses of this rock 

 is near Dudgley Cottage, about a mile north-east of All Stretton, and immediately to the east of 



