of the glacier, and consequently the sides of the ice stream become covered with fallen blocks, some of which sink through the ice, but others remain on top, forming what is called the lateral moraines. If two branches unite into one glacier, the inside lateral moraines of the two separate glaciers become the central moraine of the larger stream. If the glacier reaches a level where
Fig. 4. Diagrammatic Section through a GlacierA, Glacial cirques, or collecting grounds for the snow, filled with "névé" or "firn". B, Fallen blocks, forming a stream of stones on the side of the glacier, lateral moraine, C, Median moraine, formed by the coalescing of the lateral moraines. D, Ground moraines, formed of blocks that have worked their way to the bottom of the ice. E, Terminal moraine. The crevasses are shown.
it melts, the water, having much less carrying power than the ice, leaves the boulders behind, and the accumulation of these is called the terminal moraine. If, however, the glacier reaches the sea, the icebergs calved from off it carry the boulders out to sea frozen in them; and when the icebergs eventually melt, the boulders are dropped into the mud deposited on the sea floor. We then have a marine boulder clay or till. The terms, boulder clay or till, are otherwise used to denote any accumulation of morainic material. The boulders carried by the ice are pressed against the sides and bottom of
