C URRENT PRE- CA MBR1A N LITER A TURE S 2 3 



eruptives from rocks which have been called Huronian. It probably 

 has closer affinities to Lawson's Keewatin than to Logan's Original 

 Huronian. 



On the shores of Heron Bay the schist-conglomerate and slate were 

 examined. The conglomerate contains fragments mainly of granite. 

 These rocks are more closely allied to the Keewatin than to the Origi- 

 nal Huronian type. 



•In general it is believed that Logan mapped as Huronian, rocks 

 which are really Huronian and Keewatin. 



The ascending succession for the region as indicated by the above 

 facts is as follows : Keewatin, consisting mainly of basic green -schists; 

 Laurentian, consisting mainly of moderately acid eruptives ; and Huron- 

 ian. The term Laurentian is confined to areas of granite and granitoid 

 gneiss corresponding to the Ottawa Gneiss of eastern Canada, and hav- 

 ing eruptive relations to the Keewatin. 



The Keweenawan rocks of the various area on the north shore of 

 Lake Superior were studied, but no important conclusions were reached 

 differing from those of Irving. One variety of conglomerate, made 

 up chiefly of underlying Laurentian rocks is common on the north 

 shore, which apparently has not been found on the south shore. 



Comments. — This discussion points toward the conclusion that the 

 Original Huronian rocks of Logan are largely a series above and later 

 than certain rocks to the west mapped by Logan as Huronian, and 

 other rocks still farther to the west mapped by Lawson as Keewatin ; 

 further that the Laurentian rocks intrude the earlier series, and are 

 unconformably overlain by the later Original Huronian series of 

 Logan. 



That the Original Huronian, in large part, is younger than some of 

 the Keewatin rocks of Lawson is possible. The finding of chert and 

 jasper fragments in the conglomerate cited by Irving and Van Hise as 

 Lower Huronian would show that more of the series belongs to an 

 upper division than was supposed. 



However, as Dr. Coleman himself would fully agree, there still 

 remains evidence to indicate that rocks of both Upper and Lower 

 Huronian series are present in the Original Huronian area, and for the 

 Keewatin of Lawson the evidence is conclusive that two or more series 

 are represented. In view of this wide range of rocks in both areas, 

 and the wide separation of the areas it is unsafe at present to make a 

 definite statement concerning the relative ages of Lawson's Keewatin 



