120 On certain Pseudo-Morphous Crystals of Quartz, 



cavities oxide of iron was found, and sometimes iron pyrites, or cop- 

 per pyrites, adhering to the sides ; these were apparently deposited 

 from some of the water which had entered the crystals in some in- 

 stances ; but in others they were evidently embedded in the fluor, 

 and, adhering to the deposit of quartz, were not dissolved with the 

 former. 



Earthy carbonate of iron occurs in some cavities, mixed with 

 very minute crystals of quartz ; and I have one pseudo-morphous 

 quartz crystal, which is filled with fragments of fluor, intermixed 

 with translucent fragments of carbonate of iron, and earthy car- 

 bonate of iron, all curiously cemented together into one mass ; the 

 iron ore being rather in excess. 



I have also some hollow pseudo-morphous crystals of quartz 

 formed originally on carbonate of iron, which appear to be water- 

 tight, and yet the latter substance has, like the fluor, been abstracted. 



Besides the pseudo-morphous crystals which I have described, I 

 have some crystals of quartz in the usual pyramidal form, which 

 were found with them, and which seem to merit some notice. 

 These crystals are partly composed of a series of layers or coats of 

 quartz, arranged parallel to the sides of the original crystals which 

 they enclose. Their inner and earlier coats consist of translucent 

 and whitish quartz, alternating with each other, whilst the outer 

 and more recent coats (eight or nine in number,) are of a brownish- 

 red colour, apparently denoting the presence of much iron ochre. 

 These ferruginous coats are in many parts fractured, and rather de- 

 composed, and their edges shew that they are very distinct from each 

 other, and that they differ much in thickness — say from a tenth to 

 a fiftieth of an inch. Every one of them has a distinct series, or ra- 

 ther is composed of striated or fibrous quartz — the minute striae 

 being 'perpendicular to the planes of the crystals with which they 

 are connected. The same striated or fibrous texture is observable 

 in other specimens in which the crystals, from their translucency, 

 or milk-white colour, appear to consist of pure quartz. 



I have been induced to describe these phenomena rather fully, 

 having been struck with the resemblance between these striated 

 coats or laminae, and the fibrous quartz found in our ^^cross-courses,''^ 

 or north and south veins, which is termed " cross-course spar^ by 

 the miners. The striae of the latter are 'perpendicular to the sides 

 of the north and south veins ; and this is another circumstance in 

 which there seems to be a resemblance between them and the fibrous 

 coats of the quartz crystals. If we assume that the form and direction 

 of the latter have been determined by polarising forces more or les 

 connected with the quartz crystals which they envelope, may we not 

 infer that the corresponding phenomena, on a larger scale in the 

 north and south veins, which have been referred to, were influenced by 

 analogous forces acting in definite directions under the surface of 

 the earth I 



