Dr. Mac Culloch on the Hill of Kinnoul. 223 



greenstone. This variety is the least abundant. It occasionally 

 assumes a brownish or reddish colour, retaining its original com- 

 pactness and uniformity of texture, and thus forming a member of 

 the trap family, to which no distinct name has been assigned. This 

 becomes at times porphyritic, containing numerous minute crystals 

 of felspar imbedded in a blackish or brown basis, and forming a 

 showy variety of trap porphyry. The felspar, as far as I have 

 observed, is always opaque. Sometimes the rock is both porphy- 

 ritic and amygdaloidal, but perhaps the greater part of the whole 

 hill consists of a rock merely amygdaloidal, the base of which 

 is either the well characterized basalt above described, or that variety 

 which is less marked, or else a rock intermediate between this 

 latter and indurated clay. 



The character of the amygdaloid varies considerably according to 

 the substances which it contains, and these are green earth, calca- 

 reous spar, quartz, and chalcedony. 



Green earth or chlorite, is the substance' which perhaps occurs 

 most frequently, and it is indeed that by which the trap of Kinnoul 

 is particularly distinguished from almost all the rocks of this tribe 

 in Scotland. The nodules vary but little in size, and although they 

 are occasionally met with of the bulk of a filbert, they are gene- 

 rally little larger than a grain of mustard. But they vary much in 

 colour, assuming all shades from greenish black to the brightest 

 verdegris green. They differ equally in texture, being sometimes 

 minutely powdery, at other times of a large scaly fracture, like the 

 chlorite which occurs in primary rocks. It is this substance which 

 Faujas has called steatite ; no real steatite being found in the trap 

 of Kinnoul, although it is common in that of the island of Sky. 



When calcareous spar forms the amygdaloidal nodule, it is com- 

 monly invested with a coating of chlorite. These nodules are 



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