30 F. J. Alcock — The Athabaska Series. 



north and south shores, moreover, are to be found intru- 

 sions of a foliated norite. Along the contact of the norite 

 in one locality on the north shore is found a quartzite, 

 which, if it represented Athabaska sandstone metamor- 

 phosed by contact action, shows that the latter is older 

 than the norite intrusion. No decisive evidence was seen 

 by the writer to establish this, however. 



Age of the Series. 



The age of the Athabaska series has called forth con- 

 siderable discussion. Careful search in all the localities 

 where it is found has failed to reveal any fossils in it 

 whatever. It is, however, very probably older than the 

 Ordovician, for nowhere has the latter in this region been 

 found to be cut by diabase dikes or sills, such as intrude 

 the Athabaska series. Whether it is to be referred, how- 

 ever, to the Cambrian or to late Pre-Cambrian has, 

 however, been the chief grounds for debate. The greater 

 lithological resemblance, however, to the Keweenawan 

 sandstones of the Lake Superior region, and its associa- 

 tion with diabase intrusives and extrusives render it prob- 

 able that it is to be correlated with these rather than 

 placed in the Cambrian. 



Origin of the Series. 



The structural features displayed by the series points 

 to a continental rather than a marine origin. The fea- 

 tures in favor of such an interpretation may briefly be 

 summarized. 



The dominant feature of the series is its clastic charac- 

 ter throughout. Limestones are absent and shales which 

 form the large proportion of marine sediments are at a 

 minimum. On the other hand many deposits of known 

 continental origin consist dominantly of clastic materials 

 as for example the Newark Series of the eastern United 

 States, the Siwalik beds of India, and the Old Red Sand- 

 stone of Great Britain. 



The great areal extent of the Athabaska series and its 

 great thickness also strongly point to a subaerial origin. 

 Great areas of marine sandstones of limited thickness may 

 be found, for currents and longshore drift will trans- 

 port materials for long distances, and an advancing or 

 retreating shore line during the period of deposition 

 would tend to increase the areal extent, but under 

 such conditions a great thickness of sand could not be 



