1879.] papal [Upham. 
over the greater part of Plymouth and the entire region occupied by 
the Old Colony, including the peninsula of Cape Cod; while in the 
vicinity of Boston only small areas of these deposits are found, and 
the region consists mainly of till, or unmodified drift, accumulated by 
the ice alone, without being transported and stratified by currents of 
water. The till therefore contains all the ingredients that existed in 
the beds of loose material which had been produced by long-con- 
tinued decomposition of the rocks or gathered by previous glacial 
action, and which, with much detritus eroded from the solid ledges, 
were ploughed up and thoroughly kneaded together by this ice-sheet, 
carried southward in and beneath it, and amassed in flattened sheets 
or in steep and high, ovally rounded hills, which are finely exhibited 
in Boston and within a circuit of five to fifteen miles upon all sides of 
this city. 
Before considering these accumulations of till, it will be well to 
inquire briefly what the ice-sheet was. This we may learn in 
part from the Antarctic continent, which is now similarly covered 
by ice that extends far out to sea, and, because it is lifted up by 
the ocean and broken into bergs, terminates in a vertical wall, along 
which Sir J. C. Ross sailed four hundred and fifty miles; finding only 
one point sufficiently low to allow its upper surface to be seen from 
the masthead. Here it was a plain of snowy whiteness, reaching as 
far as the eye could see. East of Nantucket and Cape Cod, the 
marein of our ice-sheet was probably in such cliffs, extending a 
thousand miles to the east-north-east, along the line where we now 
have the remarkable submarine plateaus known as the fishing banks. 
The interior of Greenland is also covered at the present time by an 
ice-sheet, which rises steeply at its edge but soon changes to a gently 
sloping plateau, elevated above the highest peaks of the land upon 
which it lies. Dr. Hayes found the angle of ascent upon this plain 
to diminish from six to two degrees in thirty miles, at which distance 
he reached an altitude of about five thousand feet. The striated 
summits of the highest mountains of New England and New York 
show that the glacial sheet was at least a mile thick at a distance of 
two hundred miles north from its edge. Its greatest depth was much 
farther to the north, in fact beyond that part of British America 
which has been explored in respect to surface geology, and from this 
deepest portion it was pushed outward by the pressure of its own 
weight. Striae, or scratches and furrows on the bed-rock, show 
that it moved without much deviation straight forward over valleys, 
