THE 



AMERICAN JOURNAL OF SCIENCE 



[FO URTH SERIES.] 



Art. XLVIT. — Relationship between Terrestrial Gravity and 

 Observed Earth- Movements of Eastern America • by J. W. 

 Spencek."* 



Contents. 



Introduction. 



Submarine Valleys and Canons indenting the Border of the Continent. 



Relationship of observed Earth Movements and Intensity of Gravity in 

 Eastern America. 



Relationship of Terrestrial Gravity to the Deformed Beaches and Rock- 

 Barrier to Lake Ontario. 



Deficiency of Gravity in the Hudson-Champlain Valley. 



Fallacy of Post-Glacial Deformation being due to the Melting of Ice- 

 caps, shown in the Anomalies of Gravity. 



On the cause of changes of Level and Deformation. 



Summary and results. 



Introduction. 



This paper has been suggested by the remarkable charts of 

 Mr. William Bowie, delineating the results of gravity investi- 

 gations^ for at once I recognized in their anomalies a relation- 

 ship to the later earth-movements, which have long been 

 special subjects of my own studies. These determinations of 

 terrestrial gravity throw a wonderful amount of additional 

 light on at least three problems : — t, The changes of level of 

 land and sea, as proved by the occurrence of the submarine 

 canons and valleys indenting the border of the Continent ; 2, 

 the post-glacial deformation measured on the deserted beaches 

 of the Great Lakes and the cause of the rocky barrier which 

 partly obstructs the Ontario basin ; and 3, the fallacy of 

 attributing the post-Glacial deformation of the lake regions to 

 melting of the glaciers. This mere statement shows the great 

 value of knowing the intensity of gravity in studying the final 



♦Read before Phil. Soc. Wash.. D. C, May 10, 1912. 



f " Effects of Topography and Isostatic Compensation upon the Intensity 

 of Gravitv," by Wm. Bowie ; Special Pub. No. 12 (2d paper), U. S. C. & G. 

 Survey, 1912. 



Am. Jour. Sci.— Fourth Series, Vol. XXXV, No. 210.— June, 1913. 

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