26 F. J. Alcock — The Athabaska Series. 



Areal Distribution. 



The large known areas covered by the Athabaska 

 Series are three in number. The first and largest is 

 that in which it was originally described and named, ex- 

 tending along the south shore of Lake Athabaska to 

 Lake Wollaston, a distance of 250 miles, and with a width 

 in a north and south direction of probably 100 miles. 

 The second is a large V-shaped area surrounding Doo- 

 baunt lake, having a length of approximately 200 miles 

 in a north-east direction, and with a width varying to a 

 maximum of about 100 miles. The third region where 

 the series is exposed is north of lake Athabaska, where 

 it forms a number of smaller areas. The regions studied 

 by the writer include the first and more particularly the 

 third of these areas. 



Lithological Character of the Series. 



In the large area lying to the south of Lake Athabaska 

 the dominant rock type is a sandstone consisting practic- 

 ally entirely of quartz. Varieties of different degrees of 

 coarseness are found. A very common type is one con- 

 sisting of well-rounded quartz grains from two to five 

 millimeters in diameter, scattered through a finer grained 

 matrix of rounded quartz particles with diameter vary- 

 ing from -2 to -6 millimeters. Another variety consists 

 of a white sandstone made up entirely of these smaller 

 grains. Still another type contains well-rounded quartz 

 pebbles up to three inches in diameter scattered irregu- 

 larly among grains of varying degrees of coarseness. 



In places the sandstone is very hard, in places weak 

 and friable. The color varies from white to yellow, 

 weathering reddish. The beds vary in thickness from a 

 few inches up to two feet; irregular joint -planes cause 

 them to break into blocks some of huge size. 



In the areas north of Lake Athabaska the series is 

 dominantly red in color, although gray and yellow beds 

 are found locally. The rock types found in these locali- 

 ties consist of sandstone, arkose and conglomerate, with 

 interbedded flows and sills of diabase. The largest of 

 these areas is north of the Beaverlodge lakes; smaller 

 areas are found north of Spring and Maurice points, on 

 a peninsula and some islands east of Black bay, and along 

 the shore of Lake Athabaska between Sand and Big- 

 points. 



