CAJ^ADA- 331 



PART I. 



Si/nojjsis of the Evidence on icliich the Rocks of the Azoic System 

 have heen variously grouped into Distinct Divisions hy American 

 Geologists. 



In the following discussion the various regions where rocks of the 

 Azoic System occur will be taken up and examined in a geographical 

 order, beginning with that part of the North American continent where 

 these rocks have their greatest development, and where, in course of 

 a geological survey carried on continuously for more than forty years, a 

 large portion of the material has been published which will here come 

 under review. In order to prevent misunderstandings, and as an im- 

 portant assistance to those who may hereafter wish to make an inde- 

 pendent examination of the questions here discussed, the exact language 

 of the author quoted will be given in as much fulness as seems desirable, 

 although this course must necessarily considerably increase the length 

 of this paper. 



CANADA. 



Sir Wm. Logan, in the Report of Progress of the Canada Geoloszical 

 Survey for 184:5-46 (pp. 40-51), described a series of rocks which he, 

 following Lyell, called the " Metamorphic Series." This he divides into 

 two divisions, one composed in general of " syenitic gneiss," the other of 

 the same rock with intercalated bands of crystalline limestone. The 

 relations of these to each other can be best expressed in Logan's own 

 •words : — 



" To the south of the IMattawa and of the Ottawa in its continuation after 

 the junction of the two streams, important beds of crystalline limestone became 

 interstratified with the syenitic gneiss, and their presence constitutes so marked 

 a character that it appears to me expedient to consider the mass to which they 

 belong as a separate group of metamorphic strata, supposed from their geo- 

 graphical position and general attitude to overlie the previous rocks conform- 

 ably. The limestone beds appear to be fewer at the bottom than at the top 



BULL. MUS. COMP. ZOOL. VOL. VII. — NO. 11. 



