Part of Gloucestershire and Somersetshire. 367 



em is eighty fathoms,, the middle eighty-two fathoms^ and the southern, one 

 hundred and twenty-seven fathoms deep. The coal is cut out in the broad 

 way. 



§ 48. Metalliferous repositories are found in the carboniferous limestone, 

 and in the calcareous conglomerate ; and though of very different eras, both 

 contain in general calcareous spar, quartz, sulphate of baryles, galena, cala- 

 mine, brown ironstone, iron ochre, and black ironstone, with some manganese. 



The repositories of ore, in the carboniferous limestone of Mendip and 

 Broadfield Down, are beds ranging and dipping with the strata, and veins 

 intersecting the series. Both are characterized by walls of white granularly 

 foliated limestone, from which proceed on either side columnar concretions of 

 calcareous spar, meeting in the middle ; and both also sometimes consist of a 

 beautiful congeries of balls, composed of columnar concretions radiating from 

 a common centre, partly immersed in a base of granularly foliated limestone. 

 These modiBcations of carbonate of lime form the principal substance of the 

 beds and veins, and the connecting medium of the other ingredients. 



In no part of Mendip, does any trace occur of former mining operations 

 conducted upon a systematic plan ; shallow pits appearing in most places, sunk 

 near to one another, or a long line of excavations made, in open coast, at 

 the surface. In few instances are the workings supposed to have gone to any 

 considerable depth ; and the common depth perhaps rarely exceeds twenty or 

 thirty fathoms. Yet, in this manner, considerable quantities of galena and 

 calamine have been raised at different periods, in many parts of the Mendip 

 range, as well as in that of Broadfield Down. At present, little ore is raised 

 in any part of the tract. 



The calcareous conglomerate has likewise been the subject of mining 

 operations, principally in the parishes of Shipham and Roborough, and also 

 near Rickford and on Broadfield Down. The metalliferous portions of this 

 formation are traversed by veins, in all directions, sometimes in such num- 

 bers as to constitute a kind of net-work on a large scale ; the veins observ- 

 ing no regular order in the dip, but being sometimes vertical, and often inclined 

 one way or the other indifferently. They vary in width from one to six 

 inches, but are sometimes enlarged to the breadth of one, two, and three feet, 

 particularly at the points of intersection. Few v/orkings have gone to a 

 greater depth in the conglomerate than twenty or thirty fathoms, and the 

 extreme depth is said to be about thirty-five fathoms ; depending perhaps in 

 part upon the thickness of the bed of conglomerate, beyond which, in all pro- 

 bability, the veins do not penetrate into the subjacent carboniferous limestone, 

 or into the old red sandstone. 



\OL. VI. 3 B 



