Sandstone in the County of Forfar. 119 



well characterized greenstone, sometimes spotted with round 

 specks of white carbonate of lime, but these not sufficiently 

 numerous to constitute an amygdaloid. 



On the left bank some masses appear, in which compact 

 felspar with green earth predominates. 



This dike is flanked on both sides by a vertical and parallel 

 mass of altered rock, probably sandstone and shale. That on 

 the west side of the trap is very hard, and traversed by veins of 

 brown spar, and containing some green earth. It is seen on both 

 sides of the river, as is also the mass on the eastern side of the 

 dike, in which mica, quartz, and indurated ferruginous shale 

 appear, and also flesh-coloured foliated brown spar in immense 

 quantities. 



We have now descended the Carity to the point where the 

 section becomes no longer intelligible, and I have described 

 the rocks on the left bank of the river, alluding to those on 

 the right only, where they might supply an interruption, 

 which, however, they scarcely ever do, since, in each case, de- 

 composition has produced nearly the same deficiencies. 



But, in the section on the right bank, there is a want of cor- 

 respondence in one spot, which deserves our particular notice. 

 The great dike of serpentine, after being seen for 90 yards 

 on the bank, instead of coming in contact, as in the opposite 

 bank, with shale and conglomerate, is flanked by a bed of fine 

 grained greenstone, about two feet wide, from the disintegra- 

 tion of which, a hollow has been formed, down which a small 

 stream descends. 



This rock has decomposed into small spheroidal masses, 

 which, in their interior, are of a bluish black colour. Their 

 fracture is conchoidal, and they give out, when breathed up- 

 on, a strong argillaceous smell. Their outer coating is of a 

 light green colour, and very hard, and has a tendency, when 

 fractured, to present an irregularly mammillated surface. The 

 entire decomposition of this rock produces bright green and 

 yellow clays. 



An excellent account has appeared in the first number of 

 the Edinburgh Journal of Science,* by Dr MacCulloch, of a 



" Vol. I. Article i . 



