F. J. Alcock — The Athabasca Series. 29 



with a height of one-half inch. Similar markings were 

 fonnd in the Beaverlodge area. Abundant ripple- 

 marks were fonnd by Mr. Tyrrell in the sandstone in 

 Baker lake. 



Clay-balls. — South of Stone river a number of round 

 impressions filled with clay were found in the sandstone. 

 These vary in size from one to two inches in diameter, 

 and are very thin. Their method of occurrence was 

 found to be the same in every case, for they were only 

 observed in the plane between the fore-set laminae and 

 the top-set laminae of the underlying stratum. 



Folding. — South of Lake Athabaska the series lies hori- 

 zontally, or with but very slight local dips. • Its thickness 

 here as shown by barometric measurement is over 400 

 feet. In the region of the Beaverlodge lakes north of 

 Lake Athabaska, the series, however, is folded into a 

 gentle syncline in which it was found to secure a deter- 

 mination of the thickness. Over 8,000 feet of inter- 

 bedded conglomerates, arkoses and sandstones are ex- 

 posed here. This syncline has a maximum dip on the 

 limbs of 40° and pitches to the north at an angle of 20°. 

 In the other areas north of Lake Athabaska the series lies 

 practically horizontally. 



Faulting. — In the outcrop of the series near Fair point 

 excellent slickensided surfaces are preserved, which 

 shows the existence of faulting on some scale. Friction 

 breccias are present in an older quartzite series, but al- 

 though they were developed after the metamorphism of 

 this series it is unknown whether or not they were devel- 

 oped in post-Athabaskan times. Just to what extent the 

 Athabaska series was faulted is, therefore, at present 

 unknown. 



Jointing. — Jointing is marked throughout the series, 

 causing it to break into huge angular slabs. South of 

 Stone river vertical jointing in an east and west direction 

 keeps the front of the escarpment vertical while at right 

 angles to this direction large crevasses mark a second 

 joint system. The intersection of these two sets of 

 planes produces blocks of sandstone ten to twenty feet 

 across containing several hundred cubic feet of material. 

 In places these blocks stand out as vertical pillars in 

 front of the escarpment. 



Intrusion. — The series is traversed, as has already been 

 mentioned, by dykes and sills of diabase of contemporane- 

 ous age. At the eastern end of the lake on both the 



