F. J. Alcock — The Athabaska Series. 31 



deposited over an extensive area. On the other hand a 

 thick deposit of limited area might accnmnlate nnder 

 marine conditions, as for example where streams from 

 a mountainous region dump their load into deep water 

 producing what might be termed a submarine alluvial 

 fan, but such deposits must necessarily be very limited. 

 In the formation of continental deposits a change of base- 

 level affects all the rivers of the region and when aggra- 

 dation begins in one it begins in all; as a result, sub- 

 aerial deposits of practically any extent and thickness 

 may be produced. 



The character of the bedding is significant. The 

 series is uniformly thick-bedded in contrast to the regular 

 thin-bedded strata characteristic of marine deposits. 

 The presence of so much conglomerate at various hori- 

 zons and the alterations of sandstone and conglomerate 

 are also much more easily explained as fluviable than as 

 marine deposits. 



The feldspathic character of portions of the formation 

 is to be noted since it has been shown 5 that not only are 

 feldspar fragments sorted out by rivers in their progress 

 to the sea, but also wave action after the material has 

 reached the sea tends further to sort out and remove 

 the feldspar and other destructive minerals. The pres- 

 ence of the feldspar, therefore, not only indicates a sub- 

 aerial origin, but a climate during its deposition unfav- 

 orable for decomposition. 



The evidence of basic amygdaloidal and vesicular lava 

 flows interbedded with arkose is an indication of the 

 deposition of this portion of the series under subaerial 

 conditions. 



Many of the structural features point to the same con- 

 clusion. Rain-prints, sun-cracks and clay-balls are all 

 more characteristic of continental rather than marine 

 deposits. _ Though not abundant in the Athabaska 

 series, their presence in beds capable of forming and pre- 

 serving them is suggestive. The cross-bedding displayed 

 is also characteristic of water-laid, torrential deposits. 

 Local breccias are also best explained as deposits of 

 such a character. 



Conclusion. 



If we assume, therefore, that the Athabaska series is 

 of subaerial origin, then in Athabaska times, the region 

 must have been a land area with, however, an entirely 



5 MacKie, Wm. : The Sands and Sandstones of Eastern Moray, Trans. 

 Edinburgh Geol. Soc, vol. 7, pp. 148-172, 1897. 



