Englacial drift.  This name is applied to whatever debris is carried within the glacier.  It consists of rock waste fallen on the neve and there buried by accumulations of snow, and of that engulfed in the glacier where crevasses have opened beneath a surface moraine.  As the surface of the glacier is lowered by melting, more or less englacial drift is brought again to open air, and near the terminus it may help to bury the ice from view beneath a sheet of debris.

The ground moraine.  The drift dragged along at the glacier’s base and lodged beneath it is known as the ground moraine.  Part of the material of it has fallen down deep crevasses and part has been torn and worn from the glacier’s bed and banks.  While the stones of the surface moraines remain as angular as when they lodged on the ice, many of those of the ground moraine have been blunted on the edges and faceted and scratched by being ground against one another and the rocky bed.

In glaciers such as those of Greenland, whose basal layers are well loaded with drift and whose surface layers are nearly clean, different layers have different rates of motion, according to the amount of drift with which they are clogged.  One layer glides over another, and the stones inset in each are ground and smoothed and scratched.  Usually the sides of glaciated pebbles are more worn than the ends, and the scratches upon them run with the longer axis of the stone.  Why?

The terminal moraine.  As a glacier is in constant motion, it brings to its end all of its load except such parts of the ground moraine as may find permanent lodgment beneath the ice.  Where the glacier front remains for some time at one place, there is formed an accumulation of drift known as the terminal moraine.  In valley glaciers it is shaped by the ice front to a crescent whose convex side is downstream.  Some of the pebbles of the terminal moraine are angular, and some are faceted and scored, the latter having come by the hard road of the ground moraine.  The material of the dump is for the most part unsorted, though the water of the melting ice may find opportunity to leave patches of stratified sands and gravels in the midst of the unstratified mass of drift, and the finer material is in places washed away.

Glacier drainage.  The terminal moraine is commonly breached by a considerable stream, which issues from beneath the ice by a tunnel whose portal has been enlarged to a beautiful archway by melting in the sun and the warm air (Fig. 107).  The stream is gray with silt and loaded with sand and gravel washed from the ground moraine.  “Glacier milk” the Swiss call this muddy water, the gray color of whose silt proves it rock flour freshly ground by the ice from the unoxidized sound rock of its bed, the mud of streams being yellowish when it is washed from the oxidized mantle of waste.  Since glacial streams are well loaded with waste due to vigorous ice erosion, the valley in front of the glacier is commonly aggraded to a broad, flat floor.  These outwash deposits are known as valley drift.