CXXV1 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



indeed, of two different kinds, which point to differences of action, 

 as, for example, the production of a more compact combustible, 

 whether coal, anthracite, or graphite — the density being increased ; 

 or the production of a truly carbonized substance, in which more 

 or less of the volatile matter has been removed, and its density 

 diminished. M. Delesse offers some theoretical considerations on 

 the subject of this description of metamorphism. The prismatic 

 character so frequently observed he attributes to simple contraction 

 or desiccation, not requiring a very high temperature, and he cites 

 the fact, that some combustibles, when dried in the air, lose a part 

 of their volatile constituents, and assume a prismatic character : the 

 introduction of mineral matter he ascribes to filtration, aided in most 

 cases by aqueous solution, and points out how the action of trap-rocks 

 upon the usual sedimentary rocks of the earth's crust, all being 

 more or less saturated with water, must produce streams of hot 

 water, which, acting upon the rocks, will become charged with 

 saline and alkaline matter, and thus become a powerful instrument 

 of metamorphism, first by removing the volatile matter of combusti- 

 bles, and then by acting chemically upon them through the instru- 

 mentality of the matter held in solution. 



The action of heated water, penetrating either by fissures or 

 through the pores of a rock, may often explain cases of metamorphism 

 where no igneous rocks can be traced, — for example, in the Alps, as 

 quoted by M. Delesse, where combustibles of the Jurassic age have 

 been converted into anthracite. Scotland and Ireland, as well as 

 other countries, including North America, have afforded numerous 

 examples of the effects produced on rocks of various geological ages 

 and physical structure ; but, tempting as the subject is when handled 

 by M. Delesse, I shall now leave it, confidently trusting that some 

 of the able chemical philosophers of our own Society and country 

 will be induced, by what I have said, to give M. Delesse the gra- 

 tification of knowing that he has kindled enthusiasm in the minds of 

 those so fully qualified to follow his example. M. Delesse adopts the 

 same system of inquiry as Bunsen and Senft* in Germany; and I 

 hope that ere long] we shall have our own chemical geologists, in 

 Haughton, Galbraith, and others. 



The papers or essays which I have hitherto noticed afford good 

 examples of the purely chemical and physical modes of investigating 

 the condition of the earth's surface ; the one I am now about to 

 notice introduces a new principle of examination, and is peculiar to 

 our own member Mr. Sorby. The microscope has unquestionably 

 done most important service in many delicate investigations connected 

 with both inorganic and organic tissues ; and all must remember the 

 beautiful results displayed in the l Odontography' of Owen, and in 

 the works of Carpenter, Quekett, and Bowerbank : but it was reserved 

 to Mr. Sorby to apply this powerful instrument to the examination of 

 the internal structure of rocks, and to deduce from it many philo- 



* We are indebted to Mr. J. Morris for an excellent abstract, in the 'Journal,' 

 of the able work of Dr. Ferdinand Senft. It supplies what was wanting in the 

 mineralogical classification of rocks by Brongniart, namely, their chemical analysis. 



