234 RECORD OF SCIENCE FOR 1887 AND 1888. 



rate of sinking lias been estimated by Cook at 2 feet per century;* and 

 tbe obst'rvatious of the last two years corroborate this estimate. 



This land movement is not confined to the coast of New Jersey, nor 

 to historical time. It has recently been shown (1) that the entire 

 coastal plain of the Middle Atlantic slope is now undergoing- depression 

 so rapid that sedimentation in the numerous estuaries by which it is 

 dissected lags behind the sinking, so that sub-aerial alluvium is prac- 

 tically absent from the region ; (2) that the Piedmont plain overlook- 

 ing the coastal lowlands is rising so rapidly that the rivers are unable 

 to cut down their gorges to tide level ; and (3) that the differential 

 movement culminates in a line of displacement, which every river 

 crosses in a cascade or rapid, and along which the inincipal cities of 

 the eastern United States have been located.t It would appear that 

 this displacement began in early Pleistocene time, that it is yet in prog- 

 ress at a rate probably about as high as quiet orogenic movement ever 

 acquires, and that the amount of displacement increases northward from 

 perhaps 100 feet at Washington to 400 or 500 feet at New York. 



It is improbable that the great earth-movement of the Middle At- 

 lantic slope extends into New England ; for although this part of the 

 country is now suffering deformation as recently shown by Shaler, the 

 tilting is southward rather than northward as in New Jersey. The 

 modern deformation of New England is best shown in the behavior of 

 streams. Throughout Massachusetts, Connecticut, and southern New 

 Hampshire and Vermont, the greater part of the streams flow from 

 north to south or with slight deviations from this direction. Except at 

 the headwaters of these streams, where their volume is too slight to 

 clean their beds of the glacial waste which encumbers them, their 

 valleys are without swamps, and the streams flow upon beds of hard 

 rock flanked by terraces of glacial material which record the stages of 

 valley-excavation — i. e., all of these south-flowing streams have high 

 declivity and are energetically corradiug their beds. A much smaller 

 number of New England streams flow to the northward ; and these, un- 

 like their south-flowing neighbors, all flow sluggishly in d6bris-cIogged 

 valleys and are bordered by swamps instead of terraces — /. e., all of 

 these streams have low declivity and are employed in sedimentation 

 rather than corrasion. The behavior of both classes of streams sug- 

 gests southward tilting of the land and can not be satisfactorily ex- 

 plained in any other way;| and this inference is in line with the con- 

 clusions of Dana, the elder Hitchcock, and many others who have 

 shown that the southward inclination of the terraces of the Connecticut 

 Kivor and its tributaries indicates a rise of the land to the northward 

 since the recession of the last ice-sheet of the Pleistocene. It is in line, 

 too, with the work of Gilbert, Spencer, and others in the region of the 



* Geology of New Jersey, 1868, i»p. 3623-64. 



tMcGeo, 7tb Ann. Rep. U. S. Geol. Smv., 1888, pp. 616, ct seq. 



t Sbaler, Am. Jour. Sci., 1887, vol. xxxiii, pp. 210-221. 



