402 Mr. Ainsworth on the Metalliferous Veins 



Ampelite or Alum jZaie.— Extensive beds of alum-slate occur on 

 the flanks of Hartfell, at Birkhill, Kirkmichael, Evan Bridge, &c. 

 It appears to be like the ampelite of the Pyrenees, an anthracitous 

 clay-slate, intimately mixed with iron-pyrites, more or less decom- 

 posed, which may probably be referred to the white sulphuret of 

 iron of Hauy, and which Mr. Pattinson pointed out to me in the 

 metalliferous sandstones of Alston Moor. 



Flinty Slate or Siliceous Schist. — This rock occurs in consider- 

 able beds in the valley of Leadhills, and in several ravines in other 

 parts of the country. The black variety, known by the name of 

 lydian stone, is the most common. The colour of the latter ap- 

 proximates so closely to that of the rock in which it is contained, 

 that the limits of the bed can only be traced with difficulty. 



Greywacke. — I observed two varieties of this rock in the hills of 

 Dumfries : 1st, an anagenite, composed of rounded fragments of 

 quartz connected by a basis of clay-slate ; and 2d, a psephite, or 

 fragments of clay-slate imbedded in an argillaceous paste, — the lat- 

 ter contains quartz, mica, and sometimes feldspar, as accessory 

 parts. 



Greywacke-slate. — I would distinguish by this name a rock with 

 the same composition as common greywacke, and from which it is 

 only distinguished by the relative proportions of its elements, and 

 by its structure. The fragments are less, the cement more abun- 

 dant, and the whole rock has a schistose or leafy structure. Its 

 colour is ordinarily gray or grayish black, sometimes reddish : it 

 contained anthracitous fragments, mica, talc, and even pyrites, but 

 I met with no vegetable impressions. 



Compact Feldspar. — In driving a gallery through a hill near 

 the toll-bar at Wanlockhead, the workmen have cut through a bed 

 of a very compact and hard petro-siliceous rock, about three fa- 

 thoms in thickness. A similar bed occurs on the hanging side of 

 the Susanna vein, and traverses the village of Leadhills ; and this, 

 as it sometimes contains imbedded grains of grayish-coloured 

 quartz, scales of black mica, and crystals of pale flesh-coloured 

 feldspar, has been called a greenstone by Jameson. The compact 

 feldspar passes from mountain-green to yellowish-white and gray- 

 ish-white, which is the most common colour. It contains little 

 crystals of iron pyrites, but is sometimes exempt from all admix- 

 ture. This rock is met with in clay slate and in greywacke slate. 

 We find it under similar circumstances in the valley of Arran, in 

 the Pyrenees, and at Poullaouen in Bretagne ; mixed with disse- 

 minated crystals of feldspar, hornblende, schorl, and quartz, in the 

 Pyrenees, the Hartz, and in the eastern part of Upper Egypt. 

 Compact feldspar, mixed with hornblende, alternates with transi- 

 tion clay-slate at AUenborg in Sweden. 



Diorite. — Diorites or greenstones (an intimate mixture of feld- 

 spar and hornblende) are often associated with transition rocks ; 

 while dolerites (an intimate mixture of feldspar and augite) are 



