fAMi] BIBLIOGRAPHY OF CANADIAN GEOLOGY 319 



known, but they are tentatively grouped in four divisions which, begin- 

 ning with the lowest, are. Upper Ilnroniaii. Laurentian, Upper Hurou- 

 ian (?), and post-Huronian. 



At the base of the lower division of the Upper Hurouian occurs 

 a series of diorite. porphyrite, hornblende and chlorite schists. The 

 less altered, more massive varieties appear to have been gabbros and 

 may often be traced passing into the perfectly schistose types. The 

 rocks of this series are known as the '* greenstone schists," and are 

 believed to have been basic eruptives which were greatly faulted, folded 

 and metamorphosed before the post-Huronian intrusions took place. 

 Involved in the greenstone schists are certain masses which present 

 some of the characteristics of effusive bodies. 



Large areas of yreywake or feldspathic sandstone and quartzite with 

 local developments of conglomerate are present and are sometimes 

 intimately associated with the greenstone schists. The greywackes have 

 been formed mainly of volcanic ashes, they gradually pass upwards 

 into the quartzites which are undoubtedly of sedimentary origin. A 

 rock, that in the field and under the microscope closely resembles a 

 granite, occui-s over considerable areas. The field relations show that 

 this " regenerated granite " is a highly metamorphosed grey wacke or 

 feldspathic sandstone. The relative position of the conglomerate is 

 not definitely known, but it is not improbable that the succession in 

 the lower division of the Upper Huronian may be as follows : First, the 

 greenstone schists overlain by the regenerated granite and above the 

 latter quartzite, then an unconformity, and secondly, the conglomerates 

 followed by beds of greywacke passing up into quartzite. 



With the lower division of the Upper Huronian are classed certain 

 masses of gabbro or uorite or their altered forms (diorite), which are 

 intrusive into all of the foregoing rocks. These gabbros present certain 

 characteristic features which distinguished them from the post-Huronian 

 intrusives. 



The preceding Huronian rocks, with the possible exception of the 

 last mentioned gabbro type, are intruded by masses of foliated and banded 

 granitic and dioritic rocks. These are classed as Laurentian. 



Younger than all of the foregoing divisions is a formation, com- 

 posed of volcanic breccias and agglomerates overlain bj'^ bituminous 

 shales that gradually pass upwards into comparatively coarse greywacke 

 or feldspathic sandstone. These rocks, probably of Upper Huronian 

 age, appear to form a synclinal trough underlain by younger norites. 



The post-Huronian eruptives include granites, the nickel-bearing 

 eruptive and dykes of olivine diabase, the latter the youngest of all. 

 The granites are mineralogically much alike and occur in batholites. 

 These ma.sses have been formed by intrusions closely following one* 

 another and closely followed by the intrusion of norite containing the 

 nickel ore. As a result, in some places the granite mass cooled suffi- 

 ciently to allow the norite to cool against it while, in other places, 

 the acid magma was still so fluid that the contact between it and the 

 norite is marked by a rock of intermediate characters. 



The nickel-bearing eruptive varies from a uorite at its borders to 

 a handed biotite granite towards the centre of the mass. The char- 



