TRANSACTIONS OF SECTION C. 



193 



published as our knowledge has incienscd, and the age classification, haa been 

 revised.' The following classification is now employed by the Ontario Bureau^ : — ■ 



Pbe-Cambrian. 



Keweenawan 



Unconformity 



Animikean 



Under this heading are placed not only 

 the roL-ks that have heretofore been 

 called Aniniikie, but the so-called 

 Huronian rocks of the ' classic ' Lake 

 Huron area, and the Cobalt and 

 Ramsay Lake series. Minor uncon- 

 formities occur within the Animi- 

 kean. 



Great unconformity 



(Algoman granite and gneiss) 

 Igneous contact 



Laurentian of some authors, and the 

 Lorrain gi-anite of Cobalt, and the 

 Killarney granite of Lake Huron, 



etc. 



TiMISKAMIAN 



In this group are placed sedimentary 

 rocks of various localities that here- 

 tofore have been called Huronian, 

 and the Sudbury series. 



Great unconforinity 



There is no evidence that this uncon- 

 formity is of lesser magnitude than 

 that beneath the Animikean. 



(Laurentian granite and gneiss) 

 Igneous contact 



'Orenville 

 {Sedimentary) 

 Keewatin 

 (Igneous) 



Loganian 



The Grenville limestones, with more or 

 less greywacke qaiartzite 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 ai-isen 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 

 Timisknmian 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 wi-iters 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 uncon- 

 formity, 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 group of sediments, but it has 



' Ont. Bur. Mines, vol. xix., part 2; ihld., vol. xxii., part 2. 

 2 Journal of Geology, vol. xxiii., No. 7. 



