SKY. MINERALS. 40*J 



great to tempt us to seek a new place for it by this species 

 of investigation. 



The last variety exhibits a distinct crystallization ; but 

 crystals of tangible magnitude are so rare that I only 

 procured one specimen in which the forms could be deter- 

 mined. It is unnecessary to describe these as they are 

 well known to mineralogists. 



To compensate for the deficiency of large crystals of 

 this substance, a profusion of that variety is to be found, 

 which bears a general resemblance to amianthus : it is 

 popularly known in the country by the name of cotton 

 stone. These filaments occupy the cavities of the trap, 

 and are sometimes accompanied by analcime, as was 

 already remarked. They vary much in minuteness and 

 delicacy, as well as in their state of aggregation, and 

 hence many variations in their external aspect may be 

 observed. At times they are placed in distinct straight 

 needles, in other cases they are crowded into a dense 

 mass, while in a third they are so entangled as to resemble 

 a lock of cotton wool. Frequently they have the lustre 

 of common silk, with its apparent dimensions, while they 

 are in some instances so far attenuated as to resemble 

 the silk of certain spiders. When the trap has fallen into 

 powder, they are occasionally detached in light com- 

 pacted balls, which are blown away by the winds and 

 float on the surface of the water : in all these cases the 

 microscope discovers their glassy transparency, but its 

 powers are insufficient to determine their form, from the 

 dazzling play of reflected and refracted light which they 

 exhibit. In some rare instances this variety seems as if it 

 passed into the mealy ; in reality it becomes opaque and 

 puts on a mealy aspect to the naked eye ; but this is 

 readily distinguished by the lens from the specimens 

 which I have described above. The last specimens in 

 point of structure which require notice, are radiated and 

 intermixed with crystals of hornblende, producing a com- 

 pound of an unusual appearance. 



