Earth-Movements of Eastern America. 565 



view there is a deficiency of weight, extending inland, which 

 amounts to 435 feet at Charlottesville, Ya. The reduced 

 gravity in proceeding from Washington to Baltimore (where 

 it is minus 365 feet of rock) might be expected, owing to the 

 long denudation of the Susquehanna-Chesapeake valley. 



In the Great Lakes region I find that the greatest amount of 

 recent deformation is observed in passing from the zones of 

 the less rigid rocks to others more so. 



Other examples of great variation of gravity, amounting to 

 1900 feet of rock, appear between Durham and Beaufort, 

 N". C, and 1200 feet between McCormack and Charleston, 

 S. C, but this latter reduced difference might be expected, as 

 Charleston is situated much farther from the border of the 

 continental shelf than the other points mentioned. 



The anomalous intensity of gravity in Florida, especially in 

 the southeast part of the state, is of very great interest. It is 

 overweighted to even 600 feet, like the mountain zone to the 

 northward, in place of being underloaded as on the coastal 

 plain of the Carolinas. The Bahamas are, manifestly, the re- 

 mains of a great dissected coastal plain in front of Cuba, and 

 now the gravity determinations indicate that the islands and 

 coastal plains w r ere situated in front of Florida, which was a 

 backbone (although now plains), in place of their extension 

 westward over the peninsula. Thus this anomaly further dem- 

 onstrates the former continental connection of the West Indian 

 island masses. 



The intensity of gravity along the Gulf of Mexico shows 

 underloading, as is the case along the Atlantic border. But 

 it is surprising that at New Orleans there is a deficiency of 430 

 feet, in spite of the enormous load of mud being constantly 

 carried into the Gulf. Borings at New Orleans show that the 

 bottom of the old valley is not reached at 1000 feet. Prof. G. 

 D. Harris has found that several deep valleys have been cut 

 through the old Tertiary strata in Louisiana, to the west. 

 These have since been refilled with deposits containing only 

 living species of shells to depths of 2,300 feet, thus showing a 

 recent subsidence to this amount, which he thinks should reach 

 3,000 feet at the Mississippi. It may be suggested that the 

 refilling of the valley does partly account for the reduction of 

 a greater deficiency of gravity, as seen at Wilmer, a hundred 

 miles to the northeast, where it is 1,465 feet too light. 



The excess of pressure at Philadelphia is equal to 735 feet 

 of rock, but this zone is replaced at Princeton by one of defi- 

 ciency (635 feet). At New York overloading occurs to 800 

 feet, but the district on land of excessive weight is small, as if 

 the zone extended out on the continental shelf. It reappears 

 at Boston, while Maine seems to be underweighted, but this 

 region must be connected with that of the St. Lawrence river. 



