The Geognosy of Crystalline Rocks. 147 



-and carbon. On the other hand, soils which have long been 

 under arable culture are much poorer in these respects ; while 

 arable soils under conditions of known agricultural exhaustion 

 show a very low percentage of nitrogen and carbon, and a low 

 relation of carbon to nitrogen. 



In conclusion, the authors said that it had been maintained by 

 some authorities that a soil was a laboratory and not a mine ; but 

 not only the facts adduced by them in this and former papers, but 

 the history of agriculture throughout the world, so far as it was 

 known, clearly show that a fertile soil is one which had accumu- 

 lated within it the residue of ages of previous vegetation ; and 

 -that it had become infertile as this residue was exhausted. 



V. The Geognosy of Crystalline Kocks.* 



By T. Sterry Hunt. 



The author discussed at length the relations of the great masses 

 -of crystalline rocks usually divided into stratified and unstratified 

 .and considered the intrusion of the latter, both in a plastic state 

 among harder rocks, and in the form of resisting solids amono- 

 softer and yielding materials. He then proceeded to notice the 

 view held by many of the older geologists, and still entertained by 

 some, that the laminated structure in crystalline schists is no evi- 

 dence of aqueous deposition, but is developed by movements of 

 translation in a plastic igneous mass. While maintaining for most 

 stratiform rocks an origin by aqueous deposition, he showed that 

 such a structure is also developed in many cases by movements 

 during the extrusion of exotic rocks, and sought to define its con- 

 ditions. 



As regards the source of such rocks, it is argued that granites 

 and some related aggregates are (in accordance with the crenitic 

 hypothesis elsewhere advocated by the author) of secondary origin 

 and previous to their displacement had been formed from a 

 primary plutonic mass, mediately, through the action of water 

 solvents. A larger portion of exotic rocks, however, comes imme- 

 dately from this primary mass, which was itself from an early 



* Abstract of a paper read before the Royal Society of Canada at Ottawa 

 .May 28, 1885. 



