^50 NK^^' VORK STATK MUS?:!-^! 



tho luoniine. So far us chii be seen, such a l»ody of water innst 

 have l»eeM the sea, ami it would be warrantable to suppose that the 

 laud stood SO feet lower than now with reference to the ocean. 



Jamaica bay depression 

 The possibility of such deformation of the frontal plain since 

 glacial times i\& would produce the present departure from the 80 

 foot level along the northern margin is negatived by the peculiar 

 depression known as Jamaica bay, whose origin it is now necessary 

 to consider before arriving at a conclusion concerning the submer- 

 gence or non-submergence of the island at the time of the Port 

 Washington stage of ice retreat, ^ 



The semicircular area of marshes and salt creeks forming Jamaica 

 bav outlines a remarkable depression in the outwash plain. The 

 Hiomine immediately back of it is cpiite as well developed as for 

 some distance cast and west of it, nor is the crest of the moraine 

 l>erceptibly lower at this point, where there appears to be a lack 

 of development oi the plain. The moraine shows therefore no 

 signs of having been depressed at this point, and was formed prob- 

 ablv later than the depression referred tu. 



That this depression iu the plain is a feature dating from early 

 g'acial times and an original feature in the growth of the plain is 

 also shown by the behavior of the creases or drainage channels 

 which lead into the bay : these creases converge on all sides toward 

 the depression, showing that the slopes of the plain were then as 

 now toward this relatively unfilled area. It follows therefore that 

 the plain has not necessarily been deformed since glacial times, and 

 that the rising and falling of the inner line of contact of the plain 

 with the moraine is an original constructional characteristic of the 

 de|H)sits. If this reasoning be correct, then the local coincidence in 

 level of the inner margin of the plain with the level of the Port 

 Washinirt«Hi delta is not due to the control of a water level common 

 to both areas. 



Moreover there is reason to believe that the frontal plain was 

 mainly developed when the ice lay along the inner moraine pre- 

 vious to the Port AVashington stage, and, as will shortly be stated, 

 that the Port Washington delta was deposited later in a temporary 

 lake confined l>etween the moraine and the retreating ice front. 



