378 W. J. Mo Gee — Three Formations of 



the older deposit is bipartite, while the newer is indivisible ; 

 the loam of the older is unquestionably a slack water deposit, 

 while the well rounded pebbles and cobbles of the newer were 

 just as unquestionably assorted and deposited by rapid cur- 

 rents ; the older deposit rises to altitudes of 500 feet above the 

 level of the river, while the lower attains a maximum altitude 

 of only 275 feet ; the outer gorge of the Susquehanna has evi- 

 dently been excavated in obdurate paleozoic rocks since the 

 older deposit was laid down, while the work of the river since 

 the deposition of the newer has been limited to the excavation 

 of the far smaller inner gorge in unconsolidated gravels ; the 

 older deposit has been deeply dissected by .the tributary water- 

 ways, and its slopes are softened and its escarpments rounded by 

 weathering, while the same tributaries, despite their high de- 

 clivity, have cut but trifling channels in the newer deposits, and 

 the terrace scarps yet remain sharp-cut; the older deposit is 

 everywhere deeply oxidized and ferruginated and its exposed 

 bowlders of obdurate quartzite decolored and sometimes disin- 

 tegrated, while the materials of the newer deposit are fresh and 

 bright ; and the older deposit everywhere passes beneath the 

 terminal moraine into which the newer merges. 



The relation of the loam and high level bowlders to the 

 valley of the Susquehanna is significant. The river of the 

 present is commonly unnavigable, and flows in a succession of 

 rapids and intervening pools in a broad, shallow, rock-bottomed 

 channel, with an average declivity of over two and one-half 

 feet per mile : it is preeminently a transporting and corrading 

 stream ; and its local and temporary deposits are coarse, Yet 

 the loam by which the valley sides are lined is evidently a de- 

 posit of slack waters, and the associated cobbles and bowlders 

 appear to have been dropped from floes floating upon com- 

 paratively still waters ; and the altitude of the deposits pro- 

 gressively increases northward. To produce such a change in 

 the regimen of the Susquehanna as the Columbia phenomena 

 indicate would require submergence of 240 feet at its mouth 

 and fully 500 feet at the terminal moraine, and the transforma- 

 tion of its rock-bound gorge into an estuary, tidal to the Kitta- 

 tinny water-gap at least. 



The testimony of the Susquehanna phenomena corrborates 

 and supplements that recorded in the Washington deposits, in 

 that they are not only indicative of land submergence and co- 

 eval cold but prove (1) that the period of submergence was 

 one of northern glaciation, (2) that this glacial epoch was long 

 anterior to the one during which the terminal moraine was 

 formed, and (3) that the submergence increased northward. 



The Deposits on the Delaware. — As shown by the researches 

 of Lewis and Chester, at Philadelphia and in northern Dela- 



