120 On the Metamorpldc Changes ofRocTcs, ^c. 



of these singular transformations of rocks, and the hypotheses 

 they originated in their explanation, are generally much more 

 vague than the theory wliich M. Fournet has deduced from his 

 observations. The ideas of the greater number of philosophers 

 and geologists who have preceded our author, with the excep- 

 tion perhaps of those of Sir J. Hall, and Dr MacCulloch, origi- 

 nate from very different views, and are not at all supported upon 

 facts of equal value with those supplied by him. The conclu- 

 sions at which our author arrives, and the theories which he 

 deduces from them, have therefore appeared to us founded up- 

 on far more numerous observations, and much more special and 

 precise than those of his predecessors. For example, we may 

 mention, that there is in the work of which we are giving an 

 account, a suite of the most detailed observations, made upon 

 twenty-six kinds of rocks, which are traversed by the great 

 draining gallery of the mine of St Bel ; and these demonstrate 

 a perseverance and a sagacity in M. Fournet which has been 

 equalled but by few geologists. 



Two classes of considerations, as we have already remarked at 

 the beginning of this report, present themselves in the review 

 of this very important work of M. Fournet ; the former re- 

 late to the configuration of the surface, to the lines of souleve- 

 ment of its elevations, to the epochs at which these elevations 

 occurred, and to the rocks which produced them. The latter 

 are intended to demonstrate that many of the rocks which ac- 

 tually appear to be so different from each other, are really de- 

 rived from the same rock, and that they owe their differences 

 to the action of the plutonic rocks. We have nothing to ob- 

 ject to the former series. One of our number who has had 

 an opportunity of observing some of the phenomena which the 

 memoir so minutely describes, can vouch for the great accu- 

 racy of the descriptions ; and this claims our confidence for the 

 others. Wheresoever the alleged relations are admitted, the 

 merit of their discovery must be wholly conceded to M. Fournet. 



As to the second series of considerations, viz. that which re- 

 lates to the modifications stratified rocks have undergone from 

 the rocks of eruption, the generalization of their results may 

 appear to us somewhat hazardous and bold ; at all events, some 

 of them ; but the many facts which have been observed still re- 



