ANNIVERSARY ADDRESS OF THE PRESIDENT. CX1X 



the following classification as necessary to facilitate the study of so 

 comprehensive a subject : viz., 1st, normal or general metamorphism, 

 depending upon causes which have acted upon a grand scale, but 

 generally in an imperceptible manner ; 2nd, abnormal or special 

 metamorphism, which depends upon partial causes, visible in their 

 modes of action, and generally limited in extent. To this latter 

 class of metamorphism, and more especially to metamorphism of 

 contact, M. Delesse con fines his attention at present, remarking that, 

 though it is the most simple, it yet affords a vast field for inquiry ; and 

 in this restriction he acts wisely, as it cannot be doubted that the 

 safest way to arrive at a correct conclusion as to the possibility of 

 certain effects having been produced by the more obscure forces of 

 nature, is to ascertain what those forces which can be observed 

 almost in action, and which have some analogy (at least in results) 

 with the forces which may be called into action in our laboratories, 

 are capable of producing. 



M. Delesse gives a goodly list of the various European and Ame- 

 rican authors who have in some one point of view or another, as 

 M. Delesse observes, referred to the subject since the time when 

 Hutton first brought it within the range of true science ; but it 

 must be admitted that many of these authors have merely referred 

 to metamorphism as a matter of fact, and that some have occasionally 

 assumed for it powers at variance with the laws, chemical and phy- 

 sical, of nature. 



When a dyke or vein of intruded mineral matter can be so observed 

 that the portion of the rock of deposition through which it passes 

 exhibits the effect of its contact, whilst the portions distant from it 

 retain their original condition, or rather their actual condition 

 at the time of the eruption, there can be no reasonable difficulty 

 in assigning the effect to its cause, though there may yet be a 

 doubt as to the manner in which that cause had acted. One of the 

 best methods of obtaining a clue to this very obscure question is 

 to study the different effects produced on various substances by the 

 same operating cause — bearing also in mind, that here, as in every 

 exhibition of natural forces, action and reaction always accompany 

 each other, the intruded rock acting upon the mineral matter through 

 which it passes, whilst the latter reacts upon the intruded rock, the 

 two forms of metamorphism being thus called by Cotta, direct and 

 inverse, and by Fournet exomorphism and endomorphism, — cita- 

 tions which, it will be observed, I quote from M. Delesse. The effect 

 of the direct action of the erupted rock is, however, generally greater 

 than the inverse action of the rocks through which it passes, as its 

 plastic state gives it a facility in penetrating and operating upon 

 the more rigid materials of the enveloping rock, which the latter 

 does not possess. Its action also is, doubtless, assisted (as suggested 

 by M. Elie de Beaumont) by the filtration of water charged with 

 mineral matter, or by the disengagement of gaseous and vaporous 

 emanations from its mass. On this point, however, it is necessary 

 that I should observe that the abstraction of certain portions of its 

 elementary constituents from the intruded rock of eruption must 



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