Dr. Mac Culloch on the Geology of Glen Tilt, 287 



to a more minute division, many of them may perhaps also be in 

 a state of solution. On a small scale indeed examples of stony 

 matters so formed are not wanting in nature. Such are the hard 

 deposits of calcareous and other matters in water pipes, and in 

 vessels at no greater temperature than that of boiling water. It 

 is easy to see in the case of the semi-indurated strata, and of the 

 soft minerals above described, how the further abstraction of the 

 water in which these affinities were first brought into action, may 

 by increasing them in consequence of the nearer approximation of 

 the earthy particles, induce that stony hardness which these sub- 

 stances acquire in drying. 



A third and more beautiful variety of tremolite is also found 

 here. This like the last forms thin beds interposed between those 

 of the marble, and occasionally also entering as a constituent part 

 into the stone. It is that well known variety which so much 

 resembles spun glass, that this comparison forms the best description 

 that can be given of it. It is generally of a pure white colour, 

 and is radiated in stellated forms varying from an inch to two feet 

 in diameter, and exhibiting specimens of uncommon magnificence. 

 I could not perceive that. any of the specimens of this variety were 

 so decidedly flexible as the latter, although they were taken from 

 the bottom of the river, but there was still a very sensible difference 

 in their power of cutting the hands and entering into the skin 

 when first taken up, and after they had been kept for a few days. 



More rarely the same fibrous and silky variety is found passing 

 through all the shades of colour, from a pale to a very dark sea- 

 green, and these latter specimens are particularly marked by the 

 crowded and beautiful groups of their small stellated radiations. 



At no great distance from these beds and in a similar position, a 

 fourth and hitherto undescribed variety is also found, constituting a 



