1872.1] 121 [Perry. 
bore upon its back would be laid down upon the inferior drift as mo- 
rainic deposits. ‘The latter, as pertaining to the main ice-sheet, are 
comparatively limited in this country. They are strictly known as 
moraines proper. From their position they might be called the upper 
drift of the main Ice period. Being mostly composed of angular 
boulders they are often properly termed the angular erratic drift. 
The other point demanding notice relates to the phenomena pro- 
‘duced by local glaciers. These remnants of the main ice-mass were 
left in most of the elevated depressions, in which thawing would be 
tardy. As the great ice-sheet wasted, many streams of ice must have 
still remained, especially in-the high lands, filling isolated valleys, 
taking their form and direction, doing their work and effecting re- 
sults according to the lay of the region im which they prevailed. The 
main ice-mass probably having, as it dissolved, sudden ‘and long re- 
treats, followed by extended pauses, we can at once form somewhat 
of an estimate in regard to these local glaciers. | As the dissolution 
went on, the time would come when there would be only such ice- 
streams moving for the most part eastward and westward from the 
Green Mountains, and in all directions from the White Mountains, 
and finally perhaps from the White Mountains alone in New Eng- 
land. Of course these local glaciers would in places erode the un- 
derlying rocks, efface north and south striz made at an earlier time, 
and inscribe instead of them new characters of their own, and bear 
along a mass of detritus which would in many cases have a direction 
at right angles with the great continental sheet of typical drift. On 
the final melting of these isolated ice-streams, the underlying mate- 
rial would be laid bare, in the form of disguised moraines, while the 
material borne on their backs would find its place as terminal, lateral 
and medial moraines, and various other phenomena be brought to 
light, characteristic of the later Glacial times. ‘This view serves to 
explain the east-west and west-east, and other varying strize and 
evidences of smoothing already referred to, also the later drift mate- 
rial which in places overlies the main sheet, and particularly the mo- 
raines, terminal and lateral,—which are made up to a large extent of 
angular fragments from the neighboring heights, and were evidently - 
formed, not by the principal mass of ice, but by local glaciers moving 
and sometimes radiating from New England hills and mountains. 
