A contrasted type of surface moraines upon the Greenland glacier, instead of being parallel to the direction of ice movement, is directed transversely or parallel to the margins. The materials of these moraines are more rounded fragments of rock which have come up from the bottom layers, and we shall again refer to the origin of such moraines after the subglacial conditions have been considered. =The grinding mill beneath the ice.=—If, now, we examine the front of a glacier tongue which goes out from the inland ice, we find that while the upper portion is white and mainly free from rock débris (plate 13 A), the lower zone is of a dark color and crowded with layers of pebbles and bowlders which have been planed, polished, and scratched in a quite remarkable manner. The ice front is itself subject to forward and retrograde migrations of short period, but it is easily seen that in the main its larger movement has been a retrograde one. The ground from which it has lately withdrawn is generally a hard rock floor unweathered, but smooth, polished, and scratched in the same manner as the bowlders which are imbedded within the ice. It is perfectly apparent that the latter have been derived from some portion of the rock basement upon which the glacier still rests, and that floor and bowlders have alike been ground smooth by mutual contact under pressure. This erosion beneath the ice is accomplished by two processes; namely, _plucking_ and _abrasion_. Wherever the rock over which the glacier moves has stood up in projecting masses and is riven by fissure planes of any kind, the ice has found it easy to remove it in larger or smaller fragments by a quarrying process described as plucking. The rock may be said to be torn away in blocks which are largely bounded by the preëxisting fissure planes. Over relatively even surfaces plucking has little importance, but where there are noteworthy inequalities of surface upon the glacier bed, those sides which are away from the oncoming ice (_lee_ side) are degraded by plucking in such a manner as sometimes to leave steep and ragged fracture surfaces. The tools of the ice thus acquired in the process of plucking are quickly frozen into the lowest ice layers, and being now dragged along the floor they abrade in the same manner as does a rasp or file. These tools of the ice are themselves worn away in the process and are thus given their characteristic shapes. Just as the lapidary grinds the surface of a jewel into facets by imbedding the gem in a matrix, first in one and then in another position, each time wearing down the projecting irregularities through contact with the abrading surface; so in like manner the rock fragment is held fast at the bottom of the glacier until “soled” or “shod”, first upon one side and then upon another. Accidental contact with some obstruction upon the floor may suffice to turn the fragment and so expose a new surface to wear upon the abrading floor.