VEINS NEAR THE TRAP OF MOEL-Y-GOLFA, ETC. 



293 



stone, and the strike is north and south. These are the oldest strata brought to day in this neigh- 

 bourhood. The other fossil evidences collected from the shale on the flanks of the Moel-y-Golfa 

 ridge, are Euomphalus and Cardiola, of the Upper Silurian rocks. 



The most marked changes in the ordinary lithological characters of these deposits are seen all 

 along the Moel-y-Golfa and Middleton ridge, of which the Cefn is a prolonged spur. Some of the 

 most striking have been exposed by the works on the sides of the hill of Middleton, situated between 

 the Moel-y-Golfa on the south-west, and Cefn-y-Castel on the north-east. This hill is traversed by 

 several dykes of compact, light green, white and buff felspar, with minute veins of rose-coloured 

 quartz. The sides of the upper part of the hill present the appearance of irregularly stratified 

 masses, arranged in an inverted cup-form, the strata dipping inwards, and consisting of felspathic 

 sandstone and schists, alternating with felspar breccia entangling fragments of schist, similar to the 

 rocks described at Brownlow Callow near Shelve, with flakes of steatite. One of these conglomerates 

 contains rounded portions of steatite and fragments of granular felspar, another has carbonate of lime 

 diffused through grey granular felspar. These are overlaid and underlaid by bulging masses of a 

 coarse concretionary felspar rock 1 . The varieties of the felspar most uniform in structure have been 

 worked for various economical purposes, as the manufacture of china, &c. There are also large 

 veins of sulphate of barytes, with crystallized carbonate of lime, sulphuret of iron, &c. The com - 

 pact felspar passes into granular, and near the base of the hill, towards Moel-y-Golfa, some trials 

 have laid bare the large concretionary trap, as in this wood-cut. 



a. Schist. b. Amorphous trap. b*. Concretions in the trap. c. Vein of calcareous spar in the schist. 



At this spot it is well to observe, that a vein of pure white calcareous spar of about six feet in 

 width, is a few paces only distant from the trap. Will the chemist permit the speculation, that this 

 pure calcareous matter has been abstracted from the contiguous calcareous flagstone and shale by the 

 heat which accompanied the intrusion of the trap rock ? Other beds of finely laminated and indu- 

 rated sandstone are thrown off in nearly vertical positions, inclosing between them portions of the 

 same white calcareous spar. The veins (and nests) of barytes, whether in this hill or in the depres- 

 sion between Cefn-y-Castell and Builthy, have the same relations to the trap, or occupy the space 

 between the intrusive rock and the tilted, broken, and often indurated strata. They consist for the 

 most part of the sulphate, although the carbonate of barytes also appears in small quantities, with 

 occasional strings of galena. A mass of sulphate of barytes has been previously described in a 

 similar position on the western limits of the Corndon Hills, near Wotherton. At the great lead 

 mines of Snailbatch, the altered schist and sandstone contains so large a quantity of sulphate and 

 carbonate of barytes, and white calcareous spar, that the mounds of those minerals mixed with 

 quartz, &c, thrown out upon the sides of the hill, form a conspicuous object to all the adjacent 



49. 



1 The bedded felspar breccia has recently been cut into by galleries by Mr. Ryan, for the extraction of the 

 pure felspar rock. 



2 6 



