Properties of the Two New Fluids in Minerals. 413 



possible direction, and intersecting one another at angles which 

 cannot be referred to any of the crystalline forms of the mineral. 

 In a specimen of Quartz observed by Mr SOMERVILLE, and now 

 in the possession of Mr SIVRIGHT, they are arranged in hoUow 

 groupes somewhat like the cells of a honeycomb ; and when they 

 are viewed by reflected light, the corresponding faces of the ca- 

 vities are seen to be parallel, though the cavities have every pos- 

 sible variety of position with respect to each other. In other 

 specimens they form planes of variable curvature, and sometimes 

 curved surfaces of contrary flexure ; and in one specimen be- 

 longing to Mr SIVRIGHT the longitudinal cavities are grouped 

 and inflected, so as to resemble a curled lock of the finest hair, 

 as shewn in Plate XIX. Fig. 3. In a specimen of Blue Topaz 

 from Brazil, belonging to Mr SPADEN, lapidary in Edinburgh, 

 there are no fewer than four strata of cavities nearly parallel to 

 each other, and in the thickness of one-eighth of an inch. The 

 cavities have a different character in each stratum, and their num- 

 ber is such as almost to destroy the transparency of the plate. 



In the distribution of most of these groupes, accident seems to 

 have had the principal share ; but there are certain modes of 

 distribution that appear to be the result of some general prin- 

 ciple ; and a more diligent examination of them, as well as of 

 others which may yet be discovered, will probably throw farther 

 light upon the origin of this class of phenomena. In a speci- 

 men, for example, belonging to Mr SANDERSON, and shewn in 

 Plate XXI. thirteen times its natural size, an immense number of 

 cavities are arranged in rectilineal groupes, radiating from a centre 

 A. Each rectilineal group consists of two, or in some places 

 three, rows of cavities, and several of the radiations are bent from 

 their original direction. The spaces between each pair of rows 

 are filled with curiously branching cavities, some of which are 

 half an inch long ; but the remarkable fact is, that these cavities 

 are connected with numerous slender branches, many of which 



