Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/952

 is hard and massive in part, with calcareous veins and haematite, and is also amygdaloidal except where it has been exposed to the atmosphere ; it is then vesicular and in places much decomposed. An upper bed immediately beneath the limestone is very green and soft, is veined with calcite, and has also here and there a little iron pyrites ; the limestone above is very hard, and also has specks of pyrites in it. Going on now up Tideswell Dale by the private road, we soon reach the toadstone mentioned at the commencement of this paper ; and this toadstone, I am inclined to think, is of the same age as that opposite Litton Mill, although, as will be shown, it differs from it in some respects.

I will now proceed to describe the rocks as seen in the quarry (fig. 1). Beneath a thin layer of surface-soil on the slope of the hill is a bed of toadstone (a 1 ) ; the upper portion of this bed is much broken up and decomposed, and contains curious concretionary balls of all sizes, from that of a walnut up to that of a large cannon-ball ; large rounded lumps are also stated to occur in the toadstone opposite Litton Mill. Underneath this upper portion of the rock the toadstone is shattered into large blocks of indefinite shape, yellow outside from the effects of weathering, but within of a very dark green (a 2 ) ; this rock is extremely hard and dense, and will readily scratch glass. I have not analyzed it, but should consider it, judging from its appearance, to be a dolerite. In the quarry it attains a thickness of 9 or 10 feet ; this passes downwards into a coarse and much decomposed bed (a 3 ), which is partly amygdaloidal, partly vesicular, and about 2 feet thick : some of its cavities contain wad (earthy bin- oxide of manganese) in a state of fine powder ; others are filled with a mineral which has somewhat the appearance and feel of steatite.

Some of the prisms of the rock next to be described are coated with a mineral which has a similar greasy feel ; to this rock I wish to call particular attention. Immediately beneath the toadstone rocks, and without any very apparent sharp line of definition, save perhaps at one part of the quarry (where the boundary line appears rather sharper), lies a thick bed of apparently indurated red clay, at least three yards thick (b). This bed presents a very remarkable appearance, being perfectly columnar or prismatic, the prisms varying in thickness from 5 or 6 inches to about 1 inch, whilst they are about 8 or 9 feet long ; their lower ends, however, are not well seen, being buried in debris, the prisms readily breaking up and crumbling. At the north side of the quarry (fig. 1) this columnar clay presents a very strange appearance, reminding one, but for the colour of the basaltic rock, of the Giant's Causeway : the columns here attain their maximum thickness, and are well exposed for many yards, contrasting somewhat sharply with the rock above. Their position is nearly vertical, although at the bottom slightly bent. On the western side they are again seen, but are of much smaller diameter, and are inclined at an angle of 64°, whilst a little further on they lie almost horizontally, and present an appearance which was not inaptly described by one of the quarrymen as resembling a mass of corks.