Reports & Proceedings — British Association. 525 



Pre-Cambrian. 



Keweenawan 



Unconformity 



Animikean 



Under this heading are placed not only 

 the rocks that have heretofore been 

 called Animikie, but the so - called 

 Huronian rocks of the ' ' classic ' ' Lake 

 Huron area, and the Cobalt and Ramsay 

 Lake series. Minor unconformities occur 

 within the Animikean. 



Great unconformity 



{Algoman granite and gneiss) 

 Igneous contact 



Laurentian of some authors, and the 

 Lorrain granite of Cobalt, the Killarney 

 granite of Lake Huron, etc. 



TlMISKAMIAN 



In this group are placed sedimentary 

 rocks of various localities that hereto- 

 fore have been called Huronian, and 

 the Sudbury series. 



Great unconformity 



There is no evidence that this uncon- 

 formity is of lesser magnitude than 

 that beneath the Animikean. 



{Laurentian granite and gneiss) 

 Igneous contact 



{Grenville 

 {Sedimentary) 

 Keewatm 

 Igneous 



The Grenville limestones, with more or 

 less greywacke, quartzite, and iron 

 formation or jaspilyte at the base, were 

 deposited on the Keewatin lavas. 



It will be noted that the historic name " Huronian " has been 

 discarded. Much confusion has arisen through the employment of 

 this name, especially with the prefixes Upper, Middle, and Lower, in 

 different senses. The term "Lower Huronian ", for example, has 

 been applied indiscriminately to certain rocks that lie below one of 

 the greatest known unconformities — that between the Timiskamian 

 and Animikean in the table — as well as to some of those above it. 

 When making use of the term "Huronian", in order to secure 

 clearness, it has been necessary to say in what sense it is employed, 

 whether in that of the United States Geological Survey or in that of 

 various writers on the subject. 



Logan first studied the rocks, to which he afterwards gave the 

 name " Huronian ", on the shores of Lake Timiskaming. There are 

 two series of conglomerates and other fragmental rocks here, 

 separated by a great unconformity, which was discovered only when 

 the geology of the Cobalt area was worked out. The lower series 

 belongs to the Timiskamian of the table and the other to the 

 Animikean. 



The age relations of another historic series, the Grenville, have 

 also been determined only during recent years. Most authors had 

 suggested that the Grenville belonged to the so-called Huronian 



