16 



University of California Publications in Geology [Vol. 10 



9. The metamorphism of the rocks encasing the Algoman granite 

 is for rocks of pre-Laurentian age additive to an earlier metamor- 

 phism, and for rocks of post-Laurentian age not. 



SUBDIVISIONS OF TIME — NOMENCLATURE 

 Accepting now the hypothesis of two periods of granitic invasion, 

 there remains the question of nomenclature. This has to do with the 

 classification of assemblages of rocks and with the subdivision of geo- 

 logical time, and the names must be appropriate to both. I have 

 shown that pre-Cambrian epigene rocks fall into one or the other of 

 three grand divisions of time, and for these divisions it is clear that 

 we must have distinctive names. For the first or pre-Laurentian 

 division I proposed 14 many years ago the term Ontarian, and this still 

 appears to me to be the best term to adopt. It is objected by Miller and 

 Knight 15 that this term has been used as a synonym for Silurian. But 

 this synonym appears to have been stillborn ; and fortunately so, for 

 its use would be a burdensome superfluity. The word is not mentioned 

 in the recent work 10 by Schuchert on Historical Geology ; nor is it used 

 either in the text or in the tabulation of his more technical paper 17 

 presented at the Toronto meeting of the International Geological Con- 

 gress. Similarly, Ulrich appears to have no use for the term as a syno- 

 nym for Silurian in his papers. 18 If these authorities on the classifi- 

 cation of the Paleozoic and many other writers who might be cited 

 ignore the word, we may regard it as discarded and so available for 

 the use which I suggested in 1889. As for the substitute, Loganian, 

 proposed by Miller and Knight, 11 * that is effectively disbarred by the 

 general use of the name Logan for the sills of Lake Superior. 20 



Applied to the rocks formed in this period of time, Ontarian ranks 

 as a system and embraces the Coutchiching, Keewatin, and Grenville 

 series. 



For the second grand division of pre-Cambrian time the term 

 Huronian is undoubtedly the most fitting, as well as the most thor- 



14 The Internal Relations and Taxonomy of the Arehean of Central Canada, 

 Bull. Geol. Soc. Am., Dee., 1889. 



15 Eevision of pre-Cambrian Classification in Ontario, Journ. Geol., vol. 23, 

 1915. 



16 Pirsson and Schuehert, A Text-book of Geology, Part II, 1915. 



i' The Delimitation of the Geologic Period, etc., Cong. geol. internat., 1913. 

 18 E.g., Revision of the Paleozoic Systems, Bull. Geol. Soc. Am., vol. 22, pi. 

 27, 1911. 

 is Op. cit. 



20 The Laeeolithic Sills of the Northwest Coast of Lake Superior, Geol. and 

 Nat. Hist. Surv. Minn., Bull. no. 8, 1893. 



