MEMORANDUM ON GLACIER OBSERVATIONS. 
79 
extensive subsidence during the later geological periods. Further 
evidence on this question may perhaps in time be furnished by additiona 
borings, for one of which an island of the Maidive group would furnish 
an excellent locality, since there is in this case independent evidence to 
indicate that the archipelago occupies part of a sunken tract. Meantime 
any additional details would be useful, such as careful soundings around 
those atolls which have not been fully surveyed, so as to give an accurate 
profile of the seadbottom in the neighbourhood. 
MEMORANDUM ON GLACIER OBSERVATIONS. 
The recent movements of glaciers may be noted by the following 
signs 
When the ice is advancing, the glaciers generally have a more convex 
outline, the icefalls are more broken into towers and spires, and piles of 
fresh rubbish are found shot over the grass of the lower moraines. 
Moraines which have been comparatively recently deposited by advancing 
ice are disturbed, show cracks, and are obviously being pushed forward 
or aside by the glacier. 
When the ice is in retreat, the marks of its further recent extension are 
seen fringing the glacier both at the end and sides in their lower portions, 
the glacier fails to fill its former bed, and bare stony tracts, often inter¬ 
spersed with pools or lakelets, lie between the end of the glacier and the 
mounds of recent terminal moraines. 
Where a glacier has retreated to any considerable extent, careful ob¬ 
servations of the form of its bed are of value. What is the nature of the 
rock surfaces exposed-convex or concave; are they rubbed smooth on 
their leesides; how far have the contours of the cliffs or slopes, or the 
sides of any gorge, been modified where they have been subjected to ice- 
friction? Is there any evidence that the ice has flowed over large 
boulders, or loose soils, such as gravel, without disturbing them ? How 
has it affected rocks of different hardness, for instance, veins of quartz in 
a less hard rock ? Generally, do the appearances indicate that the glacier 
has excavated, or only abraded and polished its bed; that it has scooped 
