1900] Reviews. 249 



diorites or diabases in composition and representing either basic 

 segregations from the granitic magma or portions of basic intru- 

 sions caught up in it. This Fundamental Gneiss, it is beheved, 

 probably represents the original crust of the earth which has 

 undergone successive fusions and re-cementations before reaching 

 its present condition. In placing these rocks at the base of the 

 series it is not intended to assert that they stand for any distinct 

 or prolonged period of geological time, nor to affirm that these 

 rocks in their present condition and with the foliation which they 

 now possess antedate those of the Huronian system. This, as is 

 shown, is not the case in many, or even probably in most, in- 

 stances. 



The chemical and mineralogical composition of the gneisses, 

 as well as the character and origin ot their foliation and the genetic 

 relation of their associated pegmatites, are considered at length 

 and many interesting facts brought forward which cannot here he 

 further discussed. 



The Grenville Series, so extensively developed further south, 

 is is this northern area represented only by a very small and un- 

 important occurrences of highly crystalline limestone and a single 

 occurrence of gneiss. They occur isolated from one another and 

 surrounded by Fundamental Gneiss on every side, and are referred 

 to the Grenville Series on account of their identity in petrograph- 

 i cal character with the areas of this formation immediately to the 

 south. 



The district also includes large tracts of country underlain by 

 pyroclastic and epiclastic rocks, forming a northeasterly extension 

 of the development of the " typical" Huionian area on the north 

 shore of Lake Huron. At one place on Lake Temiscaming, these 

 Huronian rocks are found resting upon the floor of Fundamental 

 Gneiss on which they were originally deposited, and of whose 

 detritus they are made up ; everywhere else the Fundamental 

 Gneiss has been re-fused or softened and penetrates the superin- 

 cumbent Huronian. The total thickness of the Huronian in the 

 area is about eighteen hundred feet, made up as follows : 

 I. Breccia Conglomerate, 600 feet. 2. Shales and slaty grey- 

 wackes, 100 feet. 3. Quartzose grit or Arkose, 1 100 feet. Asso- 

 ciated with these Huronian sediments are numerous intrusions of 



