Lo7, 
When the buried ice finally disappeared under the sun’s rays the 
covering material sank, and a depression of more or less rounded 
outlined resulted (Fig. 21). The basin of Lake Ronkonkoma is 
such a kettle. 
The Ronkonkoma Moraine and its deposits do not occur at the 
surface west of Manhasset being here covered by the younger 
Harbor Hill Moraine and its associated beds, to be treated below. 
Harbor Hill Moraine 
After building the Ronkonkoma Moraine the ice receded. 
When its border had reached about the present northern shore 
of Long Island it halted and readvanced forming another morainic 
ridge, the Harbor Hill Moraine. From the Narrows to Manhasset 
the readvancing ice border pushed beyond its previous outermost 
position, overriding the northern part of the Ronkonkoma Moraine 
and associated beds. Prospect Park and the Brooklyn Botanic 
Garden are located on the Harbor Hill Moraine. 
Kast of Manhasset the younger moraine lies inside or north of 
the older moraine following for the most part the northern shore 
of the island and running out in the northern horn of eastern Long 
Island at Orient Point, and reappearing eastward at Plum Island 
and Fisher’s Island. 
On the whole, the Harbor Hill Moraine contains much more 
unassorted material, much more boulders and stones (so called 
till) than does the Ronkonkoma Moraine. In western Long Is- 
land, where the forward motion of the ice had been considerable, 
nearly all the material is stony and bouldery till. As noted in the 
first part of this Guide, there are many boulders in the moraine in 
ia 
Brooklyn Botanic Garden. 
Here in western Long Island the moraine consists of rather 
large, regular hills with fairly gentle slopes and relatively regular, 
shallow depressions. It has a width of about a mile. It rises 
from about 100 feet altitude on the Narrows to some 250 feet 
southwest of Manhasset Bay, and is from 80 to 100 feet thick.® 
— 
3The elevation of the sidewalk at the entrance gate on Eastern Parkway, 
at the north end of the Garden, is 165 feet. The elevation of the sidewall< 
at the Richard Young gate, near the south end of the Garden on Flatbush 
Ave., is approximately 80 feet—a difference of 85 feet in a distance of 3300 
feet. The elevation of Boulder Hill (in the Garden), at the Fe boulder, 
is 138 feet, or 25 feet above that of the Laboratory Plaza. 
