PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 747 



The intrusive granites and granite gneisses resemble the Laurentian. 

 They intrude the Abitibi group. The latter include a volcanic 

 complex, consisting of amphibolites and schists, chloritic rocks, 

 slate, and ferruginous dolomite; and the Pontiac series of fine- 

 grained mica schists and gneiss, hornblende schist, amphibolite, 

 arkose, graywacke, and conglomerate. 



This old complex is beveled by a pre-Cambrian peneplain 

 above which lies the Cobalt series. The contact is sharp in places; 

 in others it is gradational. The Cobalt series consists of two 

 tillite-like conglomerates separated by even-bedded graywacke, 

 argillite, quartzite, and arkose. The conglomerates are believed 

 by Wilson to be glacial because of their heterogeneous character, 

 their great extent, the size of some of the constituent bowlders, 

 the distance of some of the bowlders from the parent ledge, the 

 soled and striated nature of some of the bowlders, the improba- 

 bility that the large bowlders could have been deposited from 

 checked torrential streams, since they rest on a peneplained surface 

 on which streams must have had a low gradient. The stratified 

 deposits separating the conglomerates are believed by him to be 

 of interglacial, lacustrine origin. 



The Cobalt series are intruded by a mass of syenite porphyry 

 classed as doubtfully Keweenawan. Considered as doubtfully 

 of the same age are certain diabase dikes which cut the old complex, 

 but are not known to intrude the Cobalt series. They are called 

 the Nipissing diabase because of their lithologic similarity to the 

 Nipissing diabase of the Cobalt district. 



Wilson' presents a map and report on Timiskaming County, 

 Quebec. An outline of his classification of the pre-Cambrian 

 rocks follows. 



Keweenawan — Basic intrusives 

 Huronian — Cobalt series 



Conglomerate 



Arkose 



Graywacke and Argillite 

 Unconformity 



^ Morley E. Wilson, "Timiskaming County, Quebec," Canada Geol. Sum. Mem. 

 No. 103 (1918), 196 pp., I map. 16 pis., 6 figs. 



