28 F. J. Alcock — The Athabaska Series. 



Structural Features. 



Bedding. — Bedding is for the most part well-marked 

 throughout the series, the beds varying in thickness from 

 a few inches to two feet. Locally it is marked by color 

 banding, usually alternations of red and yellow. In 

 places, however, the texture is so uniform that the only 

 way of detecting the bedding planes is by the way the 

 rock breaks into slabs. These vary in size up to those 

 which measure ten feet across; besides those occurring 

 with outcrops in place, many are found on the sand plains 

 north of the lake. 



Cross-bedding. — The series is extensively cross-bedded, 

 in all the areas studied. South of Lake Athabaska the 

 prevailing type consists of diagonal layers bounded 

 sharply above and below by horizontal beds. The maxi- 

 mum length of the diagonal fore-set beds observed was 

 three feet. At the eastern end of the lake the slope of 

 the fore-set beds is uniformly to the south-west indicat- 

 ing a source of supply from the north-east. 



In the areas north of Lake Athabaska, the same type 

 of cross-bedding is dominant. In the small outcrops 

 between Sand and Big points, however, a more irregular 

 type is presented, snowing curved and fore-set beds, 

 irregularly truncated by other curved beds above. This 

 type, however, is on a smaller scale, and is much less 

 abundant than the variety first described. 



Sun-cracks. — Sun-cracks are not at all common 

 throughout the series ; in some fine-grained beds north- 

 east of Beaverlodge lake, some excellent examples were 

 found. The outlines were polygonal, averaging about 

 four inches in diameter, with the filling of sandstone 

 standing up as prominent ridges. Mr. Tyrrell also men- 

 tions finding sun-cracks in certain beds of Athabaska 

 sandstone in the Doobaunt lake area. The reason why 

 they are not more prevalent is evidently due to the coarse 

 clastic nature of the series which is unsuitable for their 

 development. 



Rain-prints. — Rain-prints are not common; south of 

 Stone river one layer in some fine-grained beds afforded a 

 few unmistakable examples, but aside from this no others 

 were seen. 



Ripple-marks. — Ripple marks were seen in fine-grained 

 beds in several localities. Near Fair point is an outcrop 

 where the ripple-marks were symmetrical, vary in width 

 from two to four inches measured from east to west, and 



