TRANSLATIONS AND NOTICES 



GEOLOGICAL MEMOIRS. 



Researches on the Origik of Rocks. By M. A. Delesse. 



[Bulletin de la Soc. Geol. de France, 2 e Ser. vclxv.p. 728 &c, 1858.] 



§ 1, Researches on the origin of the rocks which compose the crust 

 of the globe date from the birth of Geology itself. Based, however, 

 on very incomplete ideas, they necessarily led to error; hence the 

 most extreme doctrines have prevailed in turn. Whilst Leibnitz, 

 Descartes, Buffon, Hutton, Playfair, Sir James Hall, Dolomieu, and 

 Desmarets attribute to the eruptive rocks an igneous origin, Bernard 

 de Palissy, "Werner, Kirwan, Mohs, and Jameson assign to them an 

 aqueous origin. The volcanic rocks alone are, by common consent, 

 placed without the pale of discussion, their origin being regarded as 

 evident. In these exclusive systems, an eruptive rock is of necessity 

 formed either by water or by fire ; it seems no other alternative 

 can be admitted. 



The investigations on rocks in which for a long time I have been 

 engaged have naturally led me to the consideration of their origin. 

 This subject, so delicate, has been treated in our own tunc by eminent 

 geologists, amongst whom I may specially cite Humboldt, Erie de 

 Beaumont, Lyell, Murchison, Naumann, G. Bischoff, Dana, Daubeny, 

 Poulett Scrope, Sedgwick, Phillips, Hopkins, von Leonhard, B. Cotta, 

 Burat, Sorby, Studer, Hausmann, Boue, Keilhau, Fournet, Angelot, 

 Virlet, Durocher, Scheerer, Bunsen, and Rogers. 



The most opposite systems are still in vogue as in the first days of 

 Geology, in a way that leaves the field entirely open to conjectures ; 

 it was easy for me then to set aside every preconceived idea, and to 

 adopt the different hypotheses which accorded best with facts. I 

 purpose now to give summarily an exposition of the results at which 

 I have arrived. 



§ 2. When we go back to the origin of rocks, it is necessary to 

 investigate in the first place the different causes which have con- 

 curred in their formation. We must study, then, those which, in the 

 interior of the earth, render rocks plastic, and in general all those 

 which tend to devclopc minerals. 



These causes are : heat, water, pressure, and molecular actions. 



§ 3. Heat. — It is very evident that heat has contributed to the 

 formation of eruptive rocks. The burning volcanos which eject their 

 lavas in a state of igneous fusion give us an incontestable proof. 



VOL. XVI. PART II. I? 



