But in enumerating the evidences of glacier-action, we have to remember not only the effects produced upon the surface of the ground by the ice itself, but also the deposits it has left behind it. The loose materials scattered over the face of the earth may point as distinctly to the source of their distribution as does the character of the rocky surfaces on which they rest indicate the different causes of abrasion. In characteristic localities the loose materials deposited by glaciers may readily be recognized at first sight, and distinguished from water-worn pebbles; nor is it difficult to distinguish both from loose materials resulting from the decomposition of rocks on the spot,--the latter always agreeing with the rocks on which they rest, while the decomposition to which they owe their separation from the solid rock is often still going on. Such _debris_ are found everywhere about disintegrating rocks, and they constantly mingle with the loose fragments brought from a distance by various agencies. They are found upon and among the glacier-worn pebbles, especially where the latter have themselves been disturbed since their accumulation. They are also found among water-worn pebbles, wherever the rocky beds of our rivers or the rocky bluffs of our sea-shores crumble down. In investigating the character of loose materials transported from greater or less distances, either by the agency of glaciers or by water-currents, it is important at the very outset to discriminate between these deposits of older date and the local accessions mingling with them.