PRE-CAMBRIAN CLASSIFICATION IN ONTARIO 595 



Ontario, Moira, while other writers had given the name Killarney 

 to the granite that occurs along the north shore of Lake Huron. 

 Algoman now being preferred, although not having priority, the 

 other names may be discarded or used locally. 



Basic rocks, of pre- Algoman and post-Timiskamian age, des- 

 cribed in a preceding paragraph, are widespread, but no age 

 name is given to them in the tables. 



The age relations of the Timiskamian rocks have already been 

 described, and reasons have been given for preferring the use of 

 this name to the other that has been proposed for them. 



On a preceding page reasons have been advanced for applying 

 the name Laurentian to the pre-Timiskamian granites and gneisses 

 and not to those of post-Timiskamian age. 



The authors agree with Lawson that the Reewatin and the 

 Grenville, or Couchiching, should be grouped together. Ontarian, 

 however, should not be employed as the name of a pre-Cambrian 

 group, since the New York State geologists have long used the term 

 Ontaric (or Ontario) as synonymous with Siluric. Recognizing 

 the objection to Lawson's use of the term, we have substituted for 

 it the name Loganian, as shown in Table 11.^ 



According- to the views of the authors, the relations between 

 the Keewatin and the Grenville are as follows: The Keewatin 

 rocks represent, for the most part, submarine lava flows. On the 

 surface of these flows are deposited the Grenville sediments. 

 Moreover, it is believed that, while the major part of the Grenville 

 is later than the major part of the Keewatin, a minor part of one 

 group is contemporaneous With a minor part of the other. Hence 

 the two groups, volcanic and sedimentary respectively, are placed 

 in the authors' classification under one age term, the Loganian. 

 Lawson's Couchiching, it seems to the authors, should be corre- 

 lated with the base of the Grenville, and, since Grenville is the 

 older term, we prefer to discard Couchiching or use it only 

 locally. 



That part of the Loganian known as the Grenville is found in 

 much greater volume in southeastern Ontario and the adjacent 

 part of Quebec than in the northern and northwestern parts of the 



' Ont. Bur. Mines, XXII, Part II, Appendix. 



