Dr. Mac Culloch on the Geology of Glen Tilt. 285 



same situation may be seen thin beds of a compact pale green 

 and transparent steatite, and irregular lumps of the same substance 

 are frequently found dispersed about the beds. 



It is rare to find distinct pieces of noble serpentine of any mag- 

 nitude, but they are also met with, and of a transparency and green- 

 ness equal to that of the well known specimens from lona. 

 / Talc of various colours, white, lead-blue and green is likewise met 

 with among the marble beds, but in small quantity : and asbestus, 

 although it is seen here and there in considerable pieces, may also be 

 considered rare. But it produces abundance of tremolite, and offers 

 some interesting and uncommon varieties of that beautiful mineral. 



Of these, the first is fibrous and very compact, having a slight 

 purplish tinge, particularly when viewed according to the axis of its 

 crystallization. It is imbedded in the rock, with which it is perfectly 

 compacted, presenting on fracture a small stellated or a longer 

 radiated appearance, and giving a peculiar character to the marble. 



The next variety consists of a congeries of regular prismatic 

 crystals, varying from a tenth to a sixth of an inch in diameter. 

 These are seldom radiated, but most commonly form a dense mass 

 of which the crystals are irregularly interwoven together, and 

 sometimes curved. Thin beds of this are found between the 

 marble beds, and in some cases the crystals have shot in cavities so 

 as to present terminations, which, however formerly complete, have 

 been spoiled by the action of the water on them. 



It is well known to mineralogists that many substances when found 

 in the earth are in a soft state, and only acquire induration when 

 removed from their native beds. If we are to believe Patrin the same 

 is true even of the beryl. It is so with the tremolite which I have 

 now described, which is exceedingly soft and flexible when first 

 up, but hardens after some days of desiccation. The asbestus taken 



