25 



Miles and anc l Laurentian is seen. The interval between 

 i ome res. ^jg s ^- a ^ on anc j Schreiber is occupied entirely 

 by Laurentian rock. 



426 m. Schreiber — Altitude 993 ft. (302-6 m.). 



688-5 km. Keewatin trap extends with some interruptions 

 for about five miles (8-0 km.) west of Schreiber, 

 after which the Laurentian and Pleistocene 

 gravel deposits extend almost uninterruptedly 

 to Hartley, where the Animikie is first seen. 



From Hartley most of the rock exposures as 

 far as Port Arthur are of Animikie and Kewee- 

 nawan, with underlying Laurentian bosses. 

 Occasionally Keewatin rocks are present, but 

 these are a minor feature. Many gravel 

 deposits, exhibiting cross-bedding, occur. The 

 best views of the Animikie and Keweenawan 

 rocks are obtained near Kama, Nipigon and Red 

 Rock. 



489 m. Nipigon — Altitude 681 ft. (207-5 m )- 



787 km. 



531 m. Loon — Altitude 1,000 ft. (304-8 m.). 



854-5 km. 



THE PRE-CAMBRIAN GEOLOGY OF LOON LAKE 

 DISTRICT. 



Introduction. 



The region around Thunder bay was first described 

 geologically in a brief report by Sir W. E. Logan, (1), 

 who also gave a more extended description of the rocks 

 at a later date (2) and mapped the formations as they were 

 then known (3). Dr. R. Bell (4) explored much of this 

 region in 1869 and described many of the rocks. He also 

 prepared a map on which, however, geological boundaries 

 are lacking. The first report accompanied by a detailed 

 map was prepared by E. D. Ingall (5), who not only 

 described quite minutely the silver-bearing rocks of 

 the region, but gave a description of the silver mines. 

 Later the investigation of the iron ores of this region 

 was taken up by W. N. Smith (6, 7) upon whose work 

 the following classification of the rocks is based. 



