566 J. W. Spencer — Terrestrial Gravity and observed 



Two other areas of anomalies may here be mentioned as being 

 of relative importance in a later part of this paper. At Olym- 

 pia, Washington, a small district is overloaded by 1,100 feet, 

 while fifty miles away, at Seattle, the deficiency of gravity 

 equals 3,100 feet of rock, or a total difference of 4,200 feet. 

 The narrow coastal plain along the Pacific coast is deeply in- 

 cised with canons as on the east coast. St. Paul is in an area 

 of more than 400 miles in diameter, where the overloading 

 increases to 1,965 feet, but this is in the interior of the conti- 

 nent, yet outside this area underloading occurs over great areas. 



Relationship of Terrestrial Gravity to the Deformed Beaches 

 and Rock-barrier of Lake Ontario. 



The abandoned shorelines about the Great Lakes are found 

 to have been raised from zero to six feet per mile, in proceed- 

 ing towards the northeast and north. The investigation of 

 terrestrial gravity throws the first direct evidence as to the 

 cause of the deformation. 



The most important of the old shore-lines for determining 

 the recent earth-movements are: (1) the Iroquois Beach (of 

 the Ontario Basin),* (2) the Forest Beach of the former Lake 

 Warren (when the w r aters of the Huron, Erie and Ontario 

 basins were united at the same level), and (3) the Algonquin 

 Beach of Lake Algonquin (Lakes Huron, Michigan, and Supe- 

 rior united into one body of water), with its outlet eastward, in 

 place of by the Detroit and Niagara Rivers. f 



The present deformation of the Forest Beach, between 

 Cleveland and Font Hill (12 miles west of Niagara Falls) is 

 120 feet. This may be correlated with that of the Iroquois 

 Beach, at the head of Lake Ontario. Here it is 363 feet above 

 sea-level, but rises to 637 feet, at a point 130 miles distant, on 

 the northern side of the lake,;}: near which it becomes lost, as 

 if obstructed by a glacial dam. Following the beach around 

 the southern and eastern margins of the lake, I found that its 

 height rose to 730 feet, near Watertown. This deformation 

 of 367 feet was instrumentally measured. Beyond, the old 

 shore-line was most difficult to follow, owing to the more rug- 

 ged character of the country, but as located at Parishville,§ nine 



* This beach was first described by the writer in a paper read before the 

 Phil. Soc. Washington, Abstract in Science (1888) and published in full in 

 Trans. Eoyal Soc. Canada, vol. vii, Sec. iv, pp. 121-132, 1889. This Journal, 

 vol. xl, 1890. 



f The discovery of Lakes Warren and Algonquin, by the writer, was an- 

 nounced at the Cleveland meeting, Am. Assoc. Adv. Sc, 1888, with abstract 

 in the Proceedings, vol. xxxvii, pp. 187-199, 1889 ; this Journal, vol. xli, 

 pp. 12-21, 202-211, 1891. See " Falls of Niagara," by J. W. Spencer, Geol. 

 Surv. Can., 1907. 



JThis Journal, vol. xl, pp. 443-451, 1890. 



§ By Fairchild, and subsequently by the writer. 



