124 THE CANADIAN NATURALIST. [Dec. 



crystalline limestone is either partially or entirely of eruptive 

 origin, these calcareous veinstones having been confounded with . 

 intrusive dykes. From such veinstones a transition may be traced 

 to those in which orthoclase and quartz prevail, often to the 

 exclusion of lime and magnesia compounds. We have then true 

 o-ranite veinstones, in which tourmaline, beryl, muscovite, cassi- 

 terite and columbite are sometimes met with. These endogenous 

 rocks, in which are often concentrated the rarer chemical elements 

 of the rocks, are to be carefully distinguished from intrusive dykes 

 which are exotic rocks. Such veins are not peculiar to the 

 Laurentian system, but are found in crystalline strata at various 

 a^es. The crystalline limestones of Scandinavia, which offer so 

 many remarkable resemblances to those of New York, New Jersey 

 and Canada, are however of Laurentian age, and the nature of 

 their veias has been well understood by Scheerer. 



The rounded angles of crystals of certain minerals from the 

 calcareous veins of the Laurentian system, especially of the crystals 

 of apatite and quartz, which Emmons had supposed to be due to 

 a commencement of fusion, is to be regarded as the result of a 

 partial resolution of the previously deposited crystals, and as 

 marking a stage in the progressive filling of the veins. Crystals 

 of orthoclase, pyroxene, sphene and zircon, though accompanying 

 these rounded crystals, retain the sharpness of their angles, because 

 of their permanence in the heated alkaline solutions which circu- 

 lated through these yet partially filled veins. The various 

 minerals of these veinstones have been deposited from aqueous 

 and saline solutions, at elevated temperatures, and the experiments 

 of Daubree and of De Senarmont, and the microscopic observations 

 of Sorby, support this view. Plutonists begin to understand that 

 water cannot be excluded from rocky strata, but is all-pervading, 

 and that at greater depths, kept by pressure in a liquid state, at 

 an elevated temperature, and having its solvent powers augmented 

 by alkaline salts, it plays a most important part in metamorphosis, 

 and in the formation of veinstones. The author supposed, with 

 Mr. Hopkins, that in earlier geological periods the increase of 

 temperature in buried strata was far more rapid than at present, 

 so that great heats prevailed at comparatively small depths from 

 the surface, and produced important chemical and molecular 

 changes. The temperature at which the various silicated and 

 other minerals, including graphite, were dissolved from the strata 

 and crystallized in the veins, he supposed to have been, judging 



