27 



though the correctness of certain portions of it may be 

 questioned. To the writer it would seem that a consider- 

 able portion of the rock mapped as Lower Huronian should 

 be included in the Keewatin, particularly that situated 

 about one half mile south of Loon station, near Wylie's 

 camp. The age of the granite also may be called in question 

 by some but, if the definition of the Special Committee 

 on the Lake Superior region be accepted, it would not be 

 classed as Laurentian without some explanatory note. 



Description of Formations. 



Pleistocene. — Of this formation little can be said, 

 as no detailed work has been done toward differentiating 

 the various types of deposits, which include extensive 

 areas of glacial drift and assorted sands, clays and gravel. 



Keweenawan. — This series consists of extensive deposits 

 of conglomerates, sandstones and marls. Some writers 

 also include the Logan sills. In the area visited by the 

 excursion no extensive deposits of sandstone are seen but 

 the other features are well shown. In a cut on the Canadian 

 Pacific railway one mile west of Loon an exceptionally 

 fine outcrop of conglomerate, interbedded with small bands 

 of sandstone is exposed. The boulders of the conglomerate 

 are principally granite, though greywacke, iron formation 

 and slate (Animikie), and amphibolite also occur. This 

 conglomerate is cut by two narrow dykes of trap presum- 

 ably connected with the Logan sills. The marls and impure 

 sandstones are extensively developed near Silver lake, 

 and in these are numerous veins sometimes containing 

 sphalerite, galena and barite, but more frequently con- 

 taining amethyst. 



Possibly the most striking feature of this series is the 

 trap formation known as the Logan sills. These intrude 

 not only the older rocks but the Keweenawan as well, 

 and are referred by some writers to a later age, while 

 others look upon them as an integral part of the Keween- 

 awan. These sills seldom exhibit their intrusive nature but 

 appear as great lava sheets lying in a horizontal position 

 over the Keweenawan and Animikie. The intrusive con- 

 tact is best seen at Port Arthur, but near Loon the Animikie 

 slates and iron formation are occasionally found overlying 

 the diabase sills. 



