170 ON THE MINERAL AND METALLIFEROUS [Ch. IX. 



the lesser concretionary veins ; more commonly, however, the 

 larger veins are interposed between the boundaries of the 

 individual concretions of the rock. In the latter case, the 

 veins sometimes unite the blocks into such a firm mass, that 

 they are not separated by the action of the elements ; but, in 

 general, these veins, by being more crystalline in the middle 

 part, are readily disunited along this partially open line or 

 chain of drusy cavities : and thus it is, that we so often find one 

 or more sides of weathered rocks coated and protected by the 

 moiety of a vein ; in granite, for example, the blocks often 

 exhibit a surface of quartz, and in serpentine, of steatite or 

 asbestos. 



Proceeding still farther, we arrive at the immense masses 

 of rock resulting from the aggregation of the layers and 

 strata : on this large scale, we do not find so great a diversity 

 in the mineral composition of the veins, as in those minute 

 ones, that are confined to the concretions of rocks ; but still 

 this is in perfect keeping with the general design, for the 

 minerals which produce these rare concretionary veins, do not 

 enter into the construction of extensive masses of rocks, but 

 are confined to a few and limited localities. But, with this 

 exception, where is the line of demarcation to be drawn 

 between contemporaneous and true veins ? Mr. Carne must 

 have been convinced of this difficulty, by the establishment 

 of his order of doubtful veins, a debatable land, subject to 

 the constant inroads and reprisals of the true and contem- 

 poraneous orders ; and the best way to terminate this con- 

 tention, is by an act of union and consolidation of the 

 contending parties under one dominion : indeed, to continue 

 their separation can be but a conventionary act, for they are 

 not divided by any natural boundaries. 



It may, however, be asserted that there is a difference, 

 that true veins do not terminate in their length and depth ; 

 but the supposed nature of their origin from fissures, shows 

 that they must be limited in these directions. This opinion 

 may be traced to the miners, who have been led to this 



