492 The Formation of Cape Cod. [ August, 
Nantucket islands, from five to thirty miles farther south. A 
comparison of these with similar ranges of hills in Rhode Island, 
Long Island and New Jersey, which seem to be same series con- 
tinued farther to the west, will enable us more fully to understand 
the meaning of these deposits. 
The most noticeable product of a glacier is its terminal moraine, 
or the heaps and ridges of detritus which it brings down and 
pushes out at its end, when this remains at nearly the same place 
through a long succession of years. Slight advances and retreats 
often give these deposits a most broken surface of alternating 
hillocks and depressions, and in many cases they are partly com- 
posed of stratified gravel and sand, brought by streams during 
the meltings of summer. The great ice-sheets of the glacial 
period acted in the same way, and within a few years geologists 
have recognized the terminal moraines of that which overspread 
the Northern United States and British America. Across New 
Jersey’ and upon Long Island? its outmost border is definitely 
‚marked by a continuous series of drift-hills, one hundred and 
seventy-five miles in extent. Striz, till and boulders are confined 
_ to the region north of this line. From the Narrows to Montauk 
point this moraine is commonly known as the “ backbone of Long 
Island,” and consists of hills which vary from one hundred and 
fifty to three hundred and eighty-four feet in height. The west 
_ portion of this range, reaching from Fort Hamilton, by Green- 
wood cemetery, Prospect park and Ridgewood reservoir, to Ros- 
lyn, a distance of twenty-five miles, is mainly an unstratified 
deposit, like the loose, oxidized, angular upper till which forms 
the surface generally through New York and New England. 
From Roslyn, through the middle and east portions of the island, 
nearly all of these hills, including the highest elevations in the 
range, are composed of modified drift, being gravel and sand 
distinctly stratified and containing few or rare boulders. The ~ 
part of Long Island south of these hills consists of gently sloping 
plains of fine gravel and sand, five to ten miles in width, an 
extending a hundred miles in length. The height of their upper 
margin at the foot of the hills varies from fifty to one hundred 
1 Annual — of the Geological Survey of New Jersey for the year 1877, PP: 
9-22, with m 
2 This series sol hills on Long Island was well described by Mather in the Geolog- 
ical Report of the First District of New York, in 1843, shortly after the theory p oo 
_ continental E was pan 
