INDUSTRIAL PROGRESS DURING THE YEAR 1875. cxi 



ogy have sometimes suggested. While some of the rocks 

 of this region hitherto called greenstones are shown to 

 be eruptive rocks, many of them are hornblendic schists. 

 The intrusive granites and the el vans or quartziferous por- 

 phyries of the region are very similar in chemical and min- 

 eralogical composition. It is well known that Sorby, from 

 a study of the vacuities in the minute cavities filled with 

 liquid in the quartz of granites, endeavored, by noting the 

 temperature at which these vacuities disappear from the 

 expansion of the liquid, to calculate the temperature at 

 which such rocks solidified a result which, if established, 

 would be of great importance to science. The studies of 

 Phillips, however, confirm the previous ones of Zirkel, that 

 the volume of the bubbles in the fluid-cavities has no con- 

 stant relation to the liquid, so that we can not in this way 

 attain any certain data. Both natural and artificial crys- 

 tals contain fluid-cavities, with bubbles of various sizes, as 

 well as cavities full of liquid, and others full of gas or vapor. 

 The vein -deposits of Cornwall, carrying copper and tin 

 ores with quartz, tourmaline, chlorite, calcite, fluorine, etc., 

 have also been the subject of careful studies by Phillips, 

 who sets forth very clearly the evidences of their aqueous 

 origin ; and concludes that the repeated widenings of the 

 veins, of which there is abundant evidence, have been due 

 to the expansive force of crystallization in the fissures, as 

 long since pointed out by Hunt for the granitic veins of New 

 England. The original opening appears to have been only 

 a mere comminuted fracture of the rock in a given direction, 

 between the surfaces of which mineral substances have crys- 

 tallized from solutions, separating the fragments, and thus 

 giving rise to a brecciated vein-stone. The temperature at 

 which these materials have been deposited is supposed to 

 have been often very moderate. From the mode in which 

 quartz crystals are sometimes bent, and also from the fact 

 that in a case where the fissure in a broken mass of crystal- 

 line quartz in a Cornish vein has been filled up with tourma- 

 line, crystals of this mineral having penetrated the substance 

 of the quartz, the author ventures the supposition that the 

 quartz preserved for a time a soft and somewhat plastic con- 

 dition. From the irregular contraction of such silicious 

 masses after the solidification of the base it is suggested 



