Pseudo-Morphous Crystals of Quartz. \Vt 



I think it may be inferred, from the well-defined and smooth 

 impressions which the octohedrons of fluor have left in the quartz, 

 and the general parallelism of the sides and angles of the outer 

 cavities to those of the smaller pseudo-morphous crystals inclosed in 

 them,* that the inner and outer crystals of fluor were perfect and 

 uninjured until after the whole series of them were coated with 

 quartz. At some subsequent period then, it would appear, that 

 other changes occurred in the vein, and that the solution or destruction 

 of the fluor commenced. Some of the cavities which were found 

 to contain water only, as well as those which contained water to- 

 gether with disintegrated fluor, have the appearance of having been 

 60 hermetically sealed, that it is difficult to understand how the 

 liquid solvent could have obtained access to the fluor and abstracted 

 it from its case. It cannot be supposed that the pressure of the 

 column of water above it, although equal to more than half a ton on 

 some of the larger crystals, could alone have produced the effects ; 

 for not only must the solvent have been continually admitted through 

 the crusts of the quartz, but the salts resulting from the solution of 

 the fluor must, at the same time, have passed through them in the 

 opposite direction, a sort of endosmose and exosmose must have ex- 

 isted, as I conceive, to produce the phenomena ; whilst in other in- 

 stances, the thick envelopes of quartz were impervious, and pro- 

 tected the fluor from injury. The salts resulting from the solution 

 of the fluor must have been soluble, although this condition seems 

 to present some difficulties under the circumstances of the case ; and, 

 doubtless, the destruction of the fluor was very slowly effected in 

 many instances, and in others it was begun but never completed. 

 The diflerences in the saline contents of the water obtained from 

 some of the crystals, is another circumstance of some interest, indi- 

 cating the existence of different conditions in the vein, when the 

 water was last admitted into the respective crystals. 



The phenomena exhibited by these minerals cannot, I conceive, 

 be accounted for but by supposing the water existing in the fissures 

 of the earth, to have been changed by circulation from time to time, 

 and to have been charged with different ingredients at different 

 periods. 



I have, on former occasions, alluded to various causes which 

 would produce circulation in the subterranean waters, such as the 

 opening or closing of any portions of fissures; the ascent of warm, 

 and the descent of cooler currents of water, in consequepce of the 

 differences in their specific gravities ; or in some instances, by the 



* How are such coincidences to be accounted for.'* Are we to as- 

 sume that polarising forces have determined the arrangement ? In many 

 instances the layers of quartz which were inta-posed between the cr3stals 

 ^re very thin, imperfect, and pervious to water ; but in others they are 

 i^ot so, and some of tlie inner crystals now contain water. 



