136 ROYAL SOCIETY OF CANADA 
rentian or Ottawa gneiss is mainly, if not altogether, of eruptive origin, 
and, therefore, not a metamorphosed sediment; that the Anortho- 
sites are later eruptives; and that the Grenville is probably a true 
sedimentary series which has sagged down synclinally into the Ottawa 
gneiss on which it rests. 
The Hastings series is considered only a less crystalline phase 
of the Grenville series by Dr. Ells, and also apparently by Drs. Adams 
and Barlow; so that the Laurentian may be defined now as consisting 
of a lower eruptive group of mainly schistose rocks, the Ottawa 
gneiss; while the upper or Grenville and Hastings series are more or 
less metamorphosed sediments resting on the Ottawa gneiss and often 
nipped into it as synclines.? 
THE HURONIAN. 
The Huronian, as defined by Logan in 1863, was essentially a 
sedimentary series resting unconformably on the Laurentian. He 
describes first the rocks of Lake Temiscaming, then those of Doré 
river on Lake Superior, next those north of Lake Huron between 
Blind river and Lake Superior, giving an elaborate map founded on 
Murray’s detailed work in the region, and finally the rocks of Thunder 
bay. It has been customary to speak of the region north of Lake 
Huron as typical, since the name Huronian was derived from that 
area; but Logan gives no suggestion that he did not consider the rocks 
of Lake Superior or of Lake Temiscaming equally typical, though 
he has treated them in less detail. 
Resting unconformably on both the Laurentian and Huronian 
of the Thunder bay region is a series of black cherts and slates which 
he recognizes as distinctly later in age, the Animikie rocks of the 
present day. 
After Logan’s time Canadian geologists placed all the green schists 
and associated sedimentary rocks in the Huronian, until Dr. Lawson 
changed the nomenclature for the rocks of the Lake of the Woods 
(in 1885), and Rainy lake (in 1888), using the terms Keewatin and 
Coutchiching for upper and lower divisions of the schistose rocks 
resting on the Laurentian or nipped in as synclines between areas of 
gneiss. His reason for doing this was the apparent difference between 
the schists of western Ontario, which were largely of eruptive origin, 
and the quartzites and graywacke conglomerates north of Lake Huron, 
which were mainly sedimentary. Looking on the latter as typical 

? Origin and Relations of the Grenville and Hastings Series, Ani. Jour. 
Se., Vol. III., Mar., 1897, pp. 173-180. 
* Geol. Sur. Can., Vol. XI., 108 and 109A. 
