SUBDIVISIONS OF THE ONTARIAN SYSTEM. L83 



later formation than the schists of the Keewatin series, and breaking through 

 them. 



Irruptive Contact in Rainy Lake Region. — The studies here inaugurated 

 about Lake of the Woods have since been continued iuto the Raiuy lake 

 region, and still farther eastward to Lake Superior. A portion of the re- 

 sults are contained in a recently published report of the Geological Survey 

 of Canada.* 



Throughout this region, it was found that the Keewatin is not the only 

 group in the upper division of the Archean, but that another very volumi- 

 nous group intervenes between it and the Laurentian, to which the name 

 Coutchiching has been given.f The relations of the Laurentian to this 

 group of schists was found to be the same as to the Keewatin, with even 

 clearer and more abundant evidence of the irruptive and later origin of the 

 Laurentian. With extended observations it was also noted that the bedded 

 rocks of the Ontarian system, whether belonging to the Keewatin or Cout- 

 chiching, present a more highly altered or more crystalline and schistose 

 facies in proximity to the contact with the Laurentian granite-gneiss than in 

 the middle portions of the trough, where the rocks are frequently not greatly 

 altered from the normal character of their analogues in Paleozoic formations. 



In other words, there is evidence of contact metamorphism where the 

 Laurentian rocks come against the shattered and ragged edge of the local 

 base of the Ontarian system. All the conditions of contact, therefore, 

 whereby we recognize any mass of granite to be irruptive through stratified 

 rocks, are found to hold here between the rocks of the Laurentian and On- 

 tarian systems. The detailed geological mapping of the country shows also 

 that the Laurentian rocks, while continuous beneath the schist belts, come 

 to the surface in areas which may be described as isolated bosses. Each of 

 these is surrounded by a belt of the Ontarian rocks, usually in the form of a 

 sharply folded trough sunk down into the Laurentian and separating the 

 surface exposure of the boss from those of its neighbors. These belts of for- 

 mations of the Ontarian system are, for the most part, compact and cou- 



* Annual Report, 1887, Part F. 



fit is unfortunate that two new names have become current for this group of rocks. The term 

 i loutchiching was proposed by the writer in a paper which left his hands in March, 1887, bearing 

 that date, and which was published in the American Journal of Science in June of the same year. 

 The geological position, lithological character, known geographical distribution, relations to Kee- 

 watin and Laurentian, and ihe importance and distinct individuality of this great group, were 

 stated and discussed in that paper. In the Fifteenth Annual Report of the Geological Survey of 

 Minnesota, bearing the date of May 1, 1887, but appearing much later, there is a multitude of valu- 

 able observations and details, but no systematic statement of the geology of the region ; and the 

 differentiation of the group in question, as geologically separable from the rest of the complex, 

 does not appear to have been recognized at the time of the writing of the report, although the term 

 "Vermilion series" occurs once, apparently as an afterthought, inserted on page 299 of Professor 

 N. H. WinchelPs report. On the maps accompanying the report, however, it is distinguished 

 clearly by a color and named the " Vermilion series," although here including formations that had 

 earlier been designated Keewatin. From this it would appear that the term " Coutchiching" was 

 somewhat prior to "Vermilion," and was more fully and precisely defined as to its geological sig- 

 nificance. Moreover, the term "Vermilion Lake series" was used earlier by Irving in another 

 sense than that proposed by Professor N. H. Winchell, and in the same Annual Report (Fifteenth) 

 the terms "Vermilion series" and "Vermilion system" are used by Professor A. Winchell, on pp. 

 192, 195, 196, in another and much more comprehensive, but still undefined, sense. 



