Ch. XVI.J TO THE PREVAILING THEORY. 375 



the indications of forcible bendings can only be apparent. 

 2. Concerning the rounded and angular fragment-like portions 

 of rock which occur in some members of the primary formation, 

 we think them very different from some similar occurrences 

 among the derivative rocks, but not from all ; for they some- 

 times, like the primary, are to be attributed to concretionary 

 structure, resulting from the peculiar manner in which their 

 component parts were aggregated ; and in such cases the 

 apparent fragments are always more or less intimately united 

 with the bases by mineral transitions, or possess such frail and 

 delicate forms as are not consistent with their supposed pre- 

 vious attrition ; both of which circumstances are very dissimi- 

 lar to the ordinary condition of the nodules and fragments of 

 true conglomerates and breccia. 3. We object to the supposi- 

 tion that granite veins were originally fissures subsequently filled 

 by the injection of granite in a state of fusion on several grounds } 

 but principally on three, relating to their structure, composi- 

 tion, and interference with other veins. In form they are 

 very seldom regular, as cracks or fissures generally are, but 

 present an endless variety, both as regards their size and 

 direction, and intersect each other, in the most promiscuous 

 manner ; and, when sufficiently large to exhibit a concretion- 

 ary structure, the lines by which this is denoted sometimes 

 correspond with the sides of these veins ; but often, as at the 

 junctions of granite and slate, indiscriminately involve a larger 

 or smaller proportion of the adjacent rock. In composition, 

 they always partake more or less of the nature of the inter- 

 sected granite or slate, including portions of these rocks in 

 their course, with which, as well as with their main mass, they 

 are frequently united, by the most perfect mineral transitions ; 

 and this is not only the case, but the prophyritic crystals, 

 whether of felspar or hornblende, contained in the main mass 

 or substance of the veins, are sometimes arranged across the 

 line of junction, so as to be common both to the vein and 

 containing rock ; a bond of connection, which has also been 

 observed at the meeting of granite and slate, and which some 



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