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THE POPULAR SCIENCE MONTHLY. 



of the land or elevation of the water began in this region. Gradually 

 the sea flowed in over its shores, crept up the valleys of the streams, 

 checking their flow and converting them into tideways, until it washed 

 the base of the highlands. Up to this time the surface of the littoral 

 plain in its gradual submergence formed a broad expanse of shallow 



Fig. 6. New York Harbor in Pre-glacial Times, from South End of New York Island. 



water bounded by a monotonous line of beach, with no good harbors 

 a shifting, dangerous shore, such as is most dreaded by mariners. By 

 further subsidence, however, the water flowed up into the valleys among 

 the New York hills and into the deeper river-channels, making of the 

 first safe, landlocked harbors, of the second navigable inlets or tide- 

 ways. In this manner were produced the magnificent harbor and the 

 system of natural canals connected with it, which determined the posi- 

 tion and created the subsequent prosperity of the commercial emporium 

 of the New World. 



The subsidence which resulted in the formation of New York Har- 

 bor and its connections seems also to have affected all the coast, and 

 the influx of the sea-water filled the valleys of the rivers which drained 

 the Atlantic slope south of New York, and gave it the fringed and 

 irregular outline which constitutes its most striking characteristic. 

 James River, York River, the Potomac, the Susquehanna, and the Dela- 

 ware, are, like the Hudson, half-drowned rivers if we may use the 

 expression for all the lower portions of their valleys are estuaries, in 

 which the tide sets up to the base of the highlands. But that portion 

 of the littoral plain which separates these estuaries is too low, too 

 much cut up with water-ways, and its harbors are too shallow and ill- 



