102 REPORT OF THE SPECIAL COMMITTEE 



and the granite, was found to be absent at this locality. Two or 

 three miles east of Thessalon, felsite and granite in considerable 

 masses were found to intrude the Thessalon series. At one place 

 several felsite or granite dikes were observed to cut both the agglome- 

 rates and ellipsoidal greenstones. From the relations observed, 

 the party had no doubt that the conglomerate islands east of Thessa- 

 lon belong unconformably upon the granite, and they think it prob- 

 able (Van Hise would say highly probable) that the quartzite and 

 conglomerate rest unconformably upon the Thessalon series, mapped 

 as green chloritic slate by Logan and Murray. It is regarded as 

 probable that the white quartzite below the lower slate conglomerate 

 northwest of the Thessalon series which is adjacent, and is shown 

 by its dip to rest upon the Thessalon series, is separated from that 

 series by an unconformity, but no direct evidence of such relation 

 was observed. 



The Thessalon series should be excluded from the Huronian if, 

 as believed, the unconformity just mentioned exists. If this series 

 be excluded, the Huronian of Lake Huron consists of two series, an 

 Upper Huronian and a Lower Huronian. The Upper Huronian 

 extends from the top of the series, as given by Logan and Murray, 

 downward to and including the upper slate conglomerate; and the 

 Lower Huronian extends from the main limestone formation to the 

 gray quartzite, including its basal conglomerates. In the area 

 mapped by Logan on the north shore of Lake Huron the Laurentian 

 consists of granite and gneissoid granite, with subordinate inclusions 

 of greenstone. 



We do not feel that our examination of the Lake Superior region 

 was sufficiently detailed to warrant an attempt at correlation of the 

 individual formations of the various districts. There are, however, 

 certain general points which seem to be reasonably clear, and about 

 which there is no difference of opinion between us. These are as 

 follows : 



There is an important structural break at the base of the Keweena- 

 wan. The term "Keweenawan" should include substantially all of 

 the areas which have been thus mapped, or mapped as Nipigon, by 

 the Canadian and United States Surveys, and the State Surveys of 

 Michigan, Minnesota, and Wisconsin. 



