516 PEOCEEDII^'GS OF THE GEOLOGICAL SOCLETT. [June 6, 



The strata to be described consist of felspathic rocks, diorites, 

 serpentines, and altered limestone and calcareous grejwacke. 



II. Felspathic Eocks. 



The felspathic rocks cover a large area in the metamorphic region 

 under review. They are exceedingly well exposed along the sea- 

 coast, where they rise into rugged broken cliffs, fissured with num- 

 berless inlets and retiring coves. Very good sections are also 

 obtained in the streams that drain into the Stinchar, while the hill- 

 sides themselves are roughened with fine exposures of the same 

 rocks. These felspathic masses consist chiefly of four varieties — 

 amygdaloid, felspar-porphyry, brecciiform rocks, and finely crystal- 

 line and compact felstone, — all of which are closely related, both 

 as regards the manner of their occurrence and the mode of their 

 formation. 



A. Amygdaloid. 



The felspathic amygdaloids are largely developed throughout the 

 district, but may be best studied along shore, between Xnockgowan 

 Hill and the mouth of the river Stinchar, and at many points on the 

 coast-line north of Bennane Head. They are also very well seen at 

 numerous places along the line of fault that separates the meta- 

 morphic rocks on the north from the unaltered greywackes to the 

 south. They have, in general, an exceedingly igneous aspect, 

 especially on the coast, where they form rugged stacks, and weather 

 into rough lumpy-shaped masses on the chffs. Seen from above, 

 the igneous character of these rocks could scarcely be doubted. 

 "Where they are most typically developed, they often look as if made 

 up of large bombs — an appearance which not infrequently gives place 

 to a columnar structure. A closer inspection shows us their 

 abundant amygdaloidal cavities ; and these, taken in connexion with 

 the roughened and sometimes almost trachytic surface of the stone, 

 seem at first sight to indicate a former state of igneous fusion. 



Colour, Composition, Texture, Fracture. — The prevailing colour of 

 the amygdaloids south of the Stinchar is a pale greyish blue, passing 

 into dark green and grey ; north of Bennane Head they generally 

 assume a light purplish brown, mth occasional areas of greyish blue. 

 The matrix consists of a paste of felspathic matter, with here and 

 there a variable admixture of magnesia and lime. In texture these 

 amygdaloids sometimes resemble the felspathic traps of the Ochils, 

 the Pentlands, and other Old Red regions. This, especially, is the 

 case with those light-purplish-brown varieties which lie exposed 

 along the shore to the north of Bennane Head. The harder portions 

 of the rock show a very finely crystalline texture ; but in the more 

 alkaline and earthy areas crystals can seldom be detected, the 

 matrix appearing like a fine felspathic mud, shot here and there 

 with a few minute points of felspar. In the district south of the 

 Stinchar, the felspathic amygdaloids seldom exhibit this earthy 

 texture ; on the contrary, the matrix is harder, less alkaline, and 

 more generally crystalline, but always very finely so. The fracture 



