36 Geological Survey of Canada. 



Gneiss rock then becomes divided into two kinds, granitic and 

 syenitic gneiss, and the word gneiss wonld thus appear rather to 

 indicate the lamellar arrangement than the mineral composition. 

 Granitic and syenitic gneiss were the terms applied to these rocks 

 in the first reports ; but as granite and syenite are considered rocks 

 of igneous origin, and the epithets derived from them might be 

 supposed to have a theoretical reference to such an origin of the 

 gneiss, while at the same time it appears to me that the Lauren- 

 tian series are altered sedimentary rocks, the epithets, micaceous 

 and hornblendic have been given to the gneiss, in later reports, 

 as the best mode of designating the facts of mineral composition, 

 and lamellar arrangement, without any reference whatever to the 

 supposed origin of the rocks. When the general term gneiss 

 therefore is used, it may signify both kinds, or either ; and the 

 epithets micaceous and hornblendic are applied to the rock to in- 

 dicate that the mica greatly preponderates or excludes the horn- 

 blende, or the hornblende the mica. 



In no part of the area included in this report is hornblende 

 completely absent from the gneiss, and sometimes it predominates 

 over the mica ; hornblende contains from ten to fifteen per cent, 

 of lime, so that the ruins of the rocks of the area, such as they 

 have been described, whether gneiSs, greenstone, syenite, or por- 

 phyry, would never give a soil wholly destitute of lime. Of this 

 necessary ingredient, the lime feldspars would be a more abun- 

 dant source. Different species of them from andesin to anor- 

 thite, may contain from about five irp to twenty per cent, of lime, 

 and the range of those Canadian varieties which have been ana- 

 lyzed by Mr. Hunt, is from seven to about fifteen per cent. The 

 personal exploration which is the subject of the present report, has 

 shewn, for the first time, that these lime feldspars occur in this 

 province, and probably in other regions, in mountain ranges, be- 

 longing to a stratified deposit, and not in disseminated or intru- 

 sive masses. The breadth of these displayed in the district ex- 

 amined, demonstrates their importance ; and the fact that the 

 opalescent variety of labradorite was ascertained by Dr. Bigsby 

 to exist, in situ, on an island on the east cost of Lake Huron, 

 while the name of the mineral reminds us of its existence at the 

 eastern extremity of the Province, sufficiently points out that the 

 lineal range of the lime-feldspars will be co-extensive with Canada. 

 We may therefore anticipate a beneficial result from their influ- 

 ence upon the soils, over the whole breadth of the province. 



