of the North American Ice-Sheet. 89 
fifty to one hundred and fifty feet above the sea. Thence the 
slope gradually to sea-level at the south side of the islan 
Heights upon these plains, determined by railroad surveys, are 
as follows: Jamaica, 40 feet above sea; Mineola, 108; Hicks- 
A very ach ry cng of these deposits has been pointed 
out r. Eli i 
these “plain valleys,” as they are locally called, oceur between 
Kast New York and Riverhead, a distance of about sixty-five 
miles. In some cases they continue below our present sea- 
level and may be traced nearly across the enclosed ae to the 
beach-ridge which divides them from the open ocean; a 
that when these valleys were formed the sea at this latitude di 
water-courses crossing them, app have been formed b. 
the same floods that r 
a height about 150 feet above sea. ; 
Gardiner’s Island shows a fine exposure of these pre-glacial 
* This Journal, III, vol. xiii, pp. 142-146 and 215. 
