472 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



spinel, coruiKlum, spliene, zircon, magnetite and graphite. Some 

 of these occasionally occur in a nearly pure state filling the veins 

 as graphite, proxene and apatite. Veins of crj-stalline carbonate 

 of lime, generally including some one or more of the preceding 

 minerals are often met with, and it is these which have given rise 

 to the notion maintained in this country by Emmons, and in 

 Europe by Leonhard and others, that 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 granitic veinstones in ■ 

 which tourmaline, beryl, muscovite, cassiterite and columbite are 

 sometimes met with. These endogenous 7'ocks, in which are often 

 concentrated the rarer chemical elements of the rocks, are to be care- 

 fully distinguished from intrusive dykes which are exotic rods. 

 Such veins are not peculiar to the Laurentian system, but are found 

 in crystalline strata at various ages. The crystalline limestones of 

 Scandinavia, wdiich offer so many remarkable resemblances to 

 those of New York, New Jersey and Canada, are however of Lau- 

 rentian ajre, and the nature of their veins 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 crys- 

 tals 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 zireou, 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 miner- 

 als of these veinstones have been deposited from aqueous and 

 saline solutions at elevated temperatures, and the experiments of 

 Daubree and of De Senarmout 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 the formation of veinstones. The author supposed, w^ith Mr. 



