CONVERSION OF CARADOC SANDSTONE INTO QUARTZ ROCK. 227

above described; and in place of beds of sandstone we there find them suddenly changedinto a serrated pile of arid quartz rock of exceedingly picturesque forms, (the Sharpstones) rising to about seven hundred feet above the sea, and in which nearly alltraces of bedding have been destroyed, the lines of stratification, which can be defined,being inclined at very high angles.

Again, if we track the older strata of the same formation upon their strike from thequarries of Frodesley and the Hoar Edge, to their contact with the trap of the Little andGreat Caradoc, we meet with precisely the same phenomena, the evidence in this casebeing still more decisive. In the sandstones, at a certain distance from the trap, themechanical form of the grains of quartz is very evident, and they are associated withmuch disseminated felspar. On the north-east side of Little Caradoc, or rather betweenthat hill and the Lawley, the sandstone is thrown up in vertical beds striking nearlyeast and west, and is in a state approaching to quartz rock, being much indurated andin parts cellular, the cells frequently containing green earth and malachite; whilst on theabsolute face and summit of the trap of Little Caradoc, as well as on the eastern face ofthe Lawley, the sandstone is only to be detected in the state of true quartz rock, inmost instances the trace of bedding being entirely destroyed, and the rock resting asa thin cover or in detached fragments upon the trap. Similar masses of quartz rockadhere to the sides of these trap hills at the Battle Stones.

In one of the quartzose veins, proceeding from the Caer Caradoc, the Rev. J. Yatesdiscovered crystallized galena, an interesting fact as connected with the theory of me-tallic veins, respecting which much additional information will be communicated in thetwenty-second chapter, upon the volcanized mining tracts west of the Stiper Stones.The environs of the Caradoc alone would, however, be almost sufficient to lead us to be-lieve that veins have frequently been filled or enriched with metallic substances duringthe evolution of igneous matter through sedimentary deposits, for the altered sandstonesaround the edges of the protruding masses of trap near Hope Bowdler, are traversed tosome extent by veins of copper ore, some of which have been slightly worked at formerperiods 1 .

Without quitting the county of Salop , and restricting our observations to the vicinityof the Wrekin and the Caradoc, we are thus furnished with numerous examples ofgreat mineral changes which have taken place in these sandstones, when they are incontact with, or in the proximity of certain rocks of intrusive characters and igneousorigin, and the inference appears to be irresistible, that the sandstone has undergone thechange of composition through the action of heat, evolved during the eruption of thevolcanic matter.

1 Mr. Yates noticed vertical strata of quartz rock passing into sandstone with a vein of trap passing throughthem. He also observed malachite in the quartz rock and in those peculiar sandstones which I have termed vol-canic grit, and also in the ordinary sandstones of Long Lane quarry. Geol . Trans, vol. 2, p. 246. This mineral(green carbonate of copper) is largely disseminated in the adjoining districts to the westward. (See chapter 22.)