OF UNSTRATIFIED ROCKS AND VEINS. 163 



since they are the repositories of most of the speci- 

 mens of this substance which are to be found in mi- 

 neral collections. An enumeration of these, forms no 

 part of the present subject. In their dimensions, 

 they vary exceedingly ; the breadth reaching from 

 many yards to a thickness not exceeding that of 

 paper, and the length, or lateral extent, varying in 

 the same manner. As, however, they have no con- 

 nexions with masses of similar rocks, their termi- 

 nations in every direction can be traced, provided ac- 

 cess be obtained to these. They are subject to rami- 

 fication, and, as is elsewhere remarked, they some- 

 times follow the contortions of the strata in which 

 they are contained. 



The same description will serve for veins of calca- 

 reous carbonat ; but it must be remarked that the 

 rocks in which these occur, are much more limited. 

 They are found in limestone, in serpentine, in argil- 

 laceous schist, in shale, in some sandstones, and in 

 trap ; but are extremely rare in micaceous schist, or 

 the other rocks of the primary division : in granite 

 and gneiss, they have never, I believe, been ob- 

 served. 



The origin of these two kinds of veins has been a 

 matter of dispute among different theorists. They 

 have been called contemporaneous by one party, and 

 supposed to be produced by the same unaccountable 

 crystallization that formed the including rocks. It 

 will be time enough to examine the validity of this 

 theory when nature shall establish new laws of cry- 

 stallization, and when the past and the future are 

 alike present. Those who have favoured the theory 

 of an igneous origin or consolidation, have imagined 

 that quartz and carbonat of lime were secreted in a 

 state of fusion, into fissures formed by the shrinking 



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