SKY. GEOLOGY. TRAP VEINS. 399 



Among the trap veins selected for particular remark 

 on account of their interesting peculiarities, two are found 

 traversing the white marble of Strath. They have been 

 cut through in the operation of quarrying and are con- 

 sequently accessible for a few feet in depth ; remaining 

 in so fresh a state as to admit of a clear examination. 

 They enter together into the present excavation, but 

 immediately diverge; in such a manner however, that 

 their contact with the white marble can in many places 

 be accurately followed. Toward the interior part of 

 each, the substance is a black fine grained basalt, which 

 as it approaches the side of the vein, becomes brown 

 or greyish. At the same time its hardness diminishes 

 materially, while its boundary towards the limestone 

 becomes so irregular and uncertain, that it is often difficult 

 to determine the line that separates the two. Various 

 changes here occur, both in the composition of the trap 

 and in that of the limestone. The former, as it becomes 

 softer, is found gradually changed into a substance re- 

 sembling serpentine, and is intersected by fissures con- 

 taining laminae of steatite. Still nearer to the limestone, 

 lumps and more considerable veins of the same mineral 

 occur, lying so confusedly in both that it is difficult to 

 say with which they are most connected. If they graduate 

 into the one they seem equally to pass into the other, 

 while that part of the limestone in which they lie, changes 

 its character, becoming magnesian, argillaceous, or silice- 

 ous, and acquiring a great variety of colours. Those of the 

 steatite are various, being pale blueish grey, yellow green, 

 and dark olive green : it is besides various in quality, 

 being sometimes much indurated and at others passing 

 into transparent green serpentine. It is to this substance 

 that the white marble is indebted for the colours that 

 give rise to the numerous ornamental varieties it exhibits. 



Here therefore is an example of an intimate connexion 

 between trap and steatite, a fact which is confirmed by 

 a similar occurrence among the veins of Strathaird, the 



