Studies for Students. 



GEOLOGICAL HISTORY OF THE LAURENTIAN BASIN. 



The study of the Pleistocene history of the basin drained by 

 the St. Lawrence has been fragmentary and is still far from be- 

 ing complete. There is a lack of agreement in the interpretation 

 of observations already made, due in part to the comparatively 

 limited portion of the field examined even by those who have 

 given the subject most attention, and in part to lack of uniformity 

 in the standards of comparison used. It is with the hope of 

 assisting in reaching more harmonious results that attention is 

 here invited to methods of study. 



In the present treatment of the subject it may be advanta- 

 geously subdivided, and the facts and hypotheses relating to each 

 division separately considered. Of the divisions that may be 

 suggested the following seem the most important: 



1. Character of the sub-morainal or hard -rock topography 

 in the Laurentian basin. 



2. Origin of the basin. 

 Sedimentary deposits. 



Shore markings left by former water -bodies. 

 Fossils in ancient sediments, shore ridges, terraces, etc. 

 Fauna of the present lakes. 

 Changes in elevations of the land. 

 Former outlets. 

 Probable ejects of an ice sheet on drainage. 



10. Probable effects of a subsidence which would make the 

 basin an arm of the sea. 



I. Character of the hard -rock topography. In order to learn 

 the character of the Laurentian basin it is necessary to 



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