272 ASSINNIBOINE AND SASKATCHEWAN EXPEDITION. 



wlien bruised. The limestones of this formation do not 

 yield everywhere well crystallized minerals ; near the 

 Bay of Quinte there are beds met with which still pre- 

 serve the sedimentary character, and show only the com- 

 mencement of metamorphism. 



" The conditions in which they are sometimes found, 

 indicate that the agents which have rendered these lime- 

 stones crystalline, have been such as to render the 

 carbonate of lime almost liquid, and that, while in that 

 state, it has undergone great pressure. As evidence of 

 this opinion, we find that the limestone often fills fissures in 

 the adjacent siliceous strata, and envelopes the detached, 

 and often folded fragments of these less fusible beds 

 precisely like an igneous rock. 



" The crystalline schists, felspars, quartzites and lime- 

 stones which we have described, make up the stratified 

 portion of the Laurentian system, but there are besides, 

 intrusive granites, syenites and diorites, which form im- 

 portant masses ; the granites are sometimes albitic, and 

 often contain black tourmaline mica in large plates, zircon, 

 and sulphur et of molybdenum. 



" Among the economic minerals of this formation, the 

 ores of iron are the most important, and are generally 

 found associated with the limestones." 



In 1857 Sir William Logan read a paper before the 

 American Association for the Advancement of Science, 

 in which he referred to a former indication of a " probable 

 separation of the Laurentian rocks of Canada into two 

 great groups : that characterized by the presence of much 

 lime and that without ; " but from recent investigations 

 (previous to August, 1857) it has appeared to him " al- 

 most certain that the former of these two great groups 

 will be capable of subdivision, and that some of its bands 

 of limestone, with their associate strata, are of a sufficient 



