Chalmers — Shore Lines of the St. Lawrence Valley. 179 



to 850 feet, or 300 to 400 feet higher than similar deposits on 

 either side ; and yellow sands and gravels containing concre- 

 tions, common in the basins of Ontario and Erie lakes, were 

 observed in the marine area to the east overlying the Saxicava 

 sands and Leda clay, which must also have been carried down 

 by an overflow of the lake waters. 



1 The discussion of the causes of these oscillatory and com- 

 plementary movements will have to be reserved for the present. 

 It may be remarked, however, that it is only reasonable to 

 assume that in the folding and compression of the rocks of the 

 Northeast Appalachians along the border of the large Archean 

 area to the north, there must necessarily have been transverse 

 thrusts and uplifts along certain lines of weakness, though 

 most of these have hitherto been supposed to antedate the post- 

 Tertiary period. Three of these apparently crossed the St. 

 Lawrence basin, — one at the Thousand Islands, a second along 

 the line of igneous intrusions crossing the St. Lawrence Valley 

 at Montreal, and a third at Quebec city. 



The foregoing explanation of the phenomena is offered ten- 

 tatively, though the writer has observed all the, facts in the 

 field and feels confident that it is to geomorphic changes we 

 shall have to look for a solution of the problems presented in 

 regard to the elevated strands and the origin of the basins of 

 the Great Lakes themselves. The theory, it will be seen, 

 includes only one downward movement with three or four 

 pauses or temporary cessations of the stresses producing them, 

 and one upward movement, still in progress, the latter proved 

 to some extent by observations made by Professor G. K. 

 Gilbert of the United States Geological Survey.* The geo- 

 morphism which has taken place outside of the St. Lawrence 

 basin is not considered in this note ; it is thought, neverthe- 

 less, that the changes there will all harmonize with those out- 

 lined in this paper. It seems to the writer that the theory is a 

 more rational one, and more in accordance with observed geo- 

 logical phenomena, than that of glacial dams. The author is 

 convinced that when the history of the great changes of level 

 which have occurred in the region in question during the post- 

 Tertiary period comes to be studied more in detail, geomor- 

 phology will be found to constitute an important factor, and 

 along with denudation, enable us to explain the conformation 

 of the surface features without resort to such adventitious and 

 epigene agencies as are sometimes employed. 



Ottawa, Canada, June 22d, 1904. 



* Recent Earth Movements in the Great Lakes Region, Eighteenth Annual 

 Report, U. S. Geological Survey, 1896-7, part ii, pp. 601-647. 



