Winchell — Geological Age of the Saganaga Syenite. 387 



Minnesota Geological Survey, pp. 211-233. The prominent 

 macroscopic characters are described as follows : " wherever the 

 Saganaga syenite is traced large grains of quartz constitute a 

 distinctive character. These grains are large, angular and num- 

 erous, and on weathered surfaces stand out prominently. The 

 feldspar exists in subangular patches, imbedded with the 

 quartz in a ground mass which is mostly chloritic, and in places 

 develops chlorite spots, while in other places hornblende forms 

 emerge into visibility. So, apparently, a syenite appears or 

 disappears. These characters I have learned to recognize as. 

 the borderland between schistic and gneissic areas."* Again, 

 considerable quartz is mentioned as occurring in this rock in 

 some parts of the region. On page 215 of the same report, 

 we find it stated that white quartz is seen in considerable 

 abundance, some being in veins one or two inches in diameter, 

 but mostly resulting from the excessive abundance of the usual 

 quartz grains. These are said to be " very unevenly dissemi- 

 nated through the syenite, sometimes aggregated, and in places 

 nearly wanting. The rock itself is not of coarse a character- 

 istic syenite. All hornblende has disappeared. A feldspathic 

 matrix remains, with some green specks and spots, and the 

 quartz is imbedded in it ; some of the broken surfaces of the 

 rock have a sericitic luster. The formation on the whole 

 appears roughly bedded with a dip of 63°." The general 

 strike is N. 70° E. The syenite of Saganaga lake is also found 

 to be conglomeritic in places, and contains pebbles which are 

 strikingly similar to each other in composition and appearance. 

 They are said to be " quite uniform in lithological aspect. They 

 are uniformly dark colored, and in a rough way would be 

 called greenstones." If it were not for the difference in color 

 between the so-called pebbles and the matrix in w T hich they are 

 imbedded, we should be inclined to consider this as an agglom- 

 erate similar to those so numerous in the Keewatin and so 

 characteristic of it A majority of the ''pebbles" are com- 

 posed of lamellar augite with or without apparent small grains 

 of feldspar. There are no pebbles of syenite or jasper and no 

 sedimentary fragments. 



The significance of the facts mentioned above will become 

 apparent in the course of this paper. Before educing any con- 

 clusions from them however, it is desirable to mention a few 

 further observations made by the writer in the latter part of 

 October, 1890. The observation of greatest importance and 

 which it is believed has never before been made in this region, 

 was the discovery of a band of chalcedonic silica, one and one- 

 half inches in diameter, and about three feet in length in the 



* A. Winchell, 16 Minn. Rep., p. 214. 



