DESCRIPTION OF THE LONG ISLAND PLAIN 285 



half a mile from tbe moraine, the depressions being such as to occasion 

 swamps and even ponds. Again, the surface of the plain is covered with sev- 

 eral feet of clay loam, often stiff enough for brick clay. This is like the loam 

 over the moraine near the west end of the island and perhaps at other points. 

 The disposition of the drift south of the driftless area near New Dorp is not 

 exactly what would have been expected if it were deposited by running water. 

 Though in these minor particulars this plain departs somewhat from the 

 normal outwash plain, the departures are so slight as not to negative the 

 conclusion that such was its origin. They are enough, however, to raise the 

 query whether the plain has not been submerged to the extent of 40 feet or 

 so since the ice departed. Against this view stands the fact that distinct 

 shore features are absent. To suppose that it has been submerged is to sup- 

 pose that the submergence and subsequent emergence were accomplished with- 

 out the development of distinct shoi'e features, such as beach lines, spits, or 

 clifies." 



"Long Island. — The moraine in the Brooklyn quadrangle is everywhere bor- 

 dered on the south by a plain of stratified drift. It slopes away from the 

 moraine, at first more steeplj^ and then more gently. Its decline in the first 

 quarter of a mile is often as much as 20 feet, and a further decline of an 

 equal amount is accomplished in another mile. The moraine edge of the plain 

 has an elevation varying from 20 to 80 feet, but most commonly between 60 

 and 80 feet. So distinct is the line of junction of plain and moraine that it 

 has sometimes been interpreted as a shoreline ; but the line departs too much 

 from horizontality to bear this interpretation, unless indeed it has undergone 

 notable deformation since its de\elopment. . . . 



"Like the corresponding plain on Staten Island, this also departs in some 

 respects from the normal outwash plain. The surface of the plain is some- 

 what uneven. Elevations are less common than depressions, but neither is 

 confined to the moraine edge of the plain. . . . Another peculiar feature 

 is certain rather notable valleys and valley-like depressions which do not ap- 

 pear to be utilized by drainage at the present time. Some of them may per- 

 haps have been developed by normal drainage before the cultivation of the 

 land, but others are closed at both ends. The topography of this plain raises 

 the same questions as that of Staten Island." 



The reader will note that Salisbury evidently favors the idea of sub- 

 mergence to account for the characters of both the Staten Island and 

 Long Island plains, but is cautiously non-committal on account of the 

 absence of definite shore structures. The lack of bars, etcetera, was the 

 chief negative fact. The same difficulty was found by Shaler in his study 

 of the plains of Marthas Vineyard and Nantucket (see page 300). This 

 defect in the marine record will be satisfactorily explained in a later 

 chapter (page 299). 



The lack of horizontality or the deformation of the inner edge of the 

 plain, the evident shoreline, is exactly Avhat is required by the tilting 

 uplift of the region, clearly shown in the accompanying map of isobases, 

 plate 10. 



