Earth-Movements of Eastern America. 573 



Mountains is subordinate to the late continental subsidence, 

 and due to unequal sinking of zones resting on foundations of 

 unequal rigidity. 



In the case of the St. Lawrence region, this is in agreement 

 with the post-Glacial changes of level. In other localities this 

 is not so apparent, but suggests earlier movements that we 

 have not so far attempted to determine, which opens a new 

 and wide field. There always remain the possibilities in other 

 localities of the differences being due to masses of unequal 

 density, as in some cases have been shown by Bowie, but these 

 can be correlated in part with the physiographic features.* 



This paper must be regarded only as an advanced chapter, 

 as it is the first that has been written on the subject, with 

 only hints as to some of the bearings of the investigation. It 

 may be added that I have seen for three years, that a relation- 

 ship exists between the late deformation of the lake region and 

 the drowned valley of the St. Lawrence ; the results of my 

 researches on the subject are not yet published. Only after 

 studying the new chapter on gravity by Hayford and Bowie, 

 which is epoch-making in the science of physiography, did I 

 find that the earth-movements of the lake region, without lat- 

 eral thrusts, are subordinate to the greater continental changes 

 of level, and a satisfactory explanation of their origin. This 

 is in fulfillment of the prediction of Prof. J. P. Lesley, twenty- 

 five years ago, made on the first appearance of my paper on 

 " The Iroquois Beach of Lake Ontario," when he wrote : " It is 

 a page in the new history inaugurated in a great measure by 

 yourself, and involving some of the most important points 

 . . . and in fact must throw light on the whole subject of 

 elevation and subsidence as applicable to the entire area of the 

 United States." 



Washington, D. C, April, 1913. 



* The anomalies of gravity would be the same whether there has been an 

 increase or diminution of matter at the surface (deposition or erosion) or a 

 transference of some internal terrestrial mass in the earth's crust, adding 

 to or reducing the quantity at various points. 



