272 M. Dumont on the Classification of Rocks. 



This fact is further demonstrated in vesicles, the green 

 matter of which only partially fills the globular cavity. 



With respect to the chemical composition of the mem- 

 brane and of the nucleus of the vesicles in Vortex viridis, 

 the results of the author s researches are limited to the fol- 

 lowing facts : — The solutions of potass and of ammonia, and 

 sulphuric acid, after the extraction of the colouring matter, 

 cause the membrane to swell out, in which the nucleus can 

 no longer be recognized. The membrane becomes pale and 

 finally disappears entirely, but especially so long after boil- 

 ing. Acetic and chromic acids and alcohol do not affect the 

 membrane and the nucleus. By solution of iodine the vesicle 

 is coloured brown, the nucleus becomes more distinct, but 

 its colour is unaltered. It cannot, consequently, be assi- 

 milated to the nucleus of the vegetable chlorophyle vesicle, 

 which mostly consists of amylum. — {The Quarterly Journal 

 of Microscopical Science, No. iv., July, p. 278.) 



On the Classification of Rocks. By M. Dumont. 



In this communication M. Dumont proposes a distribution 

 of rocks and mineral deposits generally into three classes, 

 according to the mode of their formation, and the use of the 

 word Geyserian as a designation for the third of these classes. 



The chemical, as well as the physical, study of the crust 

 of the earth, is now beginning to engage a portion of that 

 attention which for some years has been almost exclusively 

 devoted to palaeontology ; nor can it be doubted that inquiries 

 which may hereafter enable the geologist to explain both the 

 physical and chemical condition of the earth's crust, are ne- 

 cessary to a right understanding of the past history of its 

 successive changes. M. Dumont appears to feel this, when 

 he suggests the threefold division of the rocks and strata 

 of the earth above mentioned, and the adoption of a new 

 designation for one of them. He observes that the terms 

 Neptunian and Plutonian cannot embrace all the forms of 

 mineral deposits. The term Neptunian naturally comprises 



