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examples of this kind of investigation that we are acquainted with, 

 though we know many cases where a similar research would be 

 equally well rewarded. 



We add M. Delesse's final theoretical conclusions. 



" When we study the phaenomena of metamorphism produced by 

 the different eruptive rocks, we find that there exists a great analogy 

 between them. 



" Thus the metamorphism of limestone is nearly the same at its 

 contact with lava, with trap, and with granite. 



" We must nevertheless recognize the fact that lava alone bears, 

 in itself and in its metamorphism, the stamp of a clearly evident 

 igneous origin. 



" Trap and the rocks which have a felspar of the sixth system for 

 a base may present at the same time traces of an igneous and an 

 aqueous action ; but, if we except basalt, the principal part is played 

 generally by an aqueous action. In fact, these rocks have often 

 produced no alteration on rocks with which they come in contact, 

 and which are nevertheless very easily decomposed by heat ; as, on 

 the other hand, they have been very fluid, not only at great depths, 

 but at the surface of the earth, on which they have been spread out 

 in immense beds, we must admit that they could become entirely 

 plastic without being actually reduced to a state of igneous fusion. 

 I am induced to believe that they are susceptible of forming with 

 water, aided by pressure and even by a moderate heat, a perfectly 

 fluid muddy paste, which might be compared to a mortar ; it is only 

 in becoming crystalline and in losing a part of its water that this 

 can assume its hardness and its great cohesion. 



" On the other hand, we have seen that granite, when even it has 

 been erupted in a fluid state, has not always caused an alteration in 

 the rocks over which it has been poured out, nor in those which it 

 traverses in the form of veins. The metamorphism at its contact 

 is in every case very different from that of lavas. Consequently 

 we must necessarily admit that granite can, like trap, become plas- 

 tic without passing through igneous fusion such as we know occurs 

 in lavas. 



" These theoretical conclusions are, it is true, far removed from 

 the ideas which are generally adopted as to the origin of the erup- 

 tive rocks ; they appear to me, nevertheless, to be immediately de- 

 ducible from the studies which we have now made on metamor- 

 phism." 



FuUy agreeing with M. Delesse on the very remarkable fact of the 

 slight metamorphic action sometimes exercised by even large masses 

 of igneous rocks on such matters as limestone or coal with which 

 they come in contact, and not denying the probability of the pre- 

 sence of water or vapour in many if not in all cases of subterranean 

 igneous action, we yet cannot let the above remarks pass without a 

 word of caution. The continental geologists in general seem to 

 neglect, to a dangerous extent, the important subject of denudation, 

 by which so many once deeply-seated rocks have been brought to 

 the surface. We hold it impossible for any one to show a case of 



