430 Dana — Long Island Sound in the Quaternary Era. 



sprinkled with bowlders ; and below, there is usually a layer 10 

 to 150 feet thick of bowlder clay or till, which in some parts is 

 very stony, suggesting the idea to E. Lewis, Upham, Chamberlin 

 and others, that the island is the course lengthwise of a part of 

 the continental terminal moraine. 



But the south-side plain, which slopes from about 100 feet 

 to the sea-level, has no bowlders over it in any part ; instead, 

 the material is a fine yellowish gravel nearly or quite to 

 the sea-level, as shown by facts from well-diggings." The 

 Cretaceous or other clays are cut off: short. 



The long drainage-area at the head of Peconic Bay also, al- 

 though having a range of high land and "terminal moraine" 

 both on its north and south sides, and hence lying right in the 

 teeth of the "moraine," has similar characters — yellowish 

 gravel and no bowlders. All the bowlders and stones that 

 dropped over these regions, if there were any — and they may 

 have been as many and as large as elsewhere — are now con- 

 cealed by the gravel. 



The facts may be understood if we regard the drainage area 

 extending westward from the head of Peconic Bay as the course 

 of a large valley occupied by the river which now, in dwin- 

 dled form, empties into the bay, and that the gravel deposits 

 are Quaternary beds of the Champlain period (that of melting 

 and deposition), laid down over the earlier bowlder deposits. 

 The same explanation will answer also for the region of the 

 south-side plain where the ocean may have made at the time 

 large encroachments and thus chiselled off the Cretaceous or 

 Tertiary beds. Its yellow gravel is post-glacial, notwithstand- 

 ing its resemblance to iNew Jersey pre-glacial deposits, color 

 being here, as commonly, of no chronological value. 



It is thus rendered probable that during the Glacial period 

 Long Island Sound, instead of being, as it is now, an arm of 

 the ocean twenty miles wide, was for the greater part of its 

 length a narrow channel serving as a common trunk for the 

 many Connecticut and some small Long Island streams, and 

 that the southern Sound river reached the ocean through Pe- 

 conic Bay. Under these circumstances the supply of fresh 

 water for the Sound river would have been so great that salt 

 water would have barely passed the entrance of the Sound. 



* I am indebted to a recent letter from Mr. E. Lewis (dated Brooklyn, Sept. 11, 

 for the following facts: — 



Wells have been dug or bored along the plains — near the old Central R. R. — 

 quite down to tide level. No Cretaceous, or any other deep beds of clay have 

 been found so far as I know. The earth passed through has been sand and gravel 

 in layers down as far as the wells have gone, except here and there some very 

 thin clayey beds, mere crusts which are, I believe, only isolated pockets. The 

 Bethpage bed does not extend southward beneath the plain, but northward. The 

 same is true of similar beds at Deer Park, some six miles eastward. These are 

 overlaid with drift. They form the front or southward edge of the hills and 

 occur some 15 feet down at the base of the hills. 



