II. The SUPERFICIAL ACCUMULATIONS embrace a wide-spread class of geological phenomena. These have originated in causes some of which are still in active operation, others are dormant, and others again may be considered as belonging to agencies which may be termed extraordinary, or permitted only at intervals to display themselves. The effects of their operations are visible, less or more, in every part of the surface of the globe. They have been termed the PLEISTOCENE group, and consist of both marine and fresh water materials. To these are referred the bowlder-clay formation, the vast deposits of sand and gravel heaped up in valleys, the erratic blocks spread over hill-tops, and the various kinds of detrital matter which, although often laminated, is loose and unstratified, and clearly distinguishable from the more indurated and subjacent beds composing the earth’s crust. Nor in gathering up the links of this extended field of review, will it be possible to omit all mention of glaciers and their moraines, so intimately connected with Alpine scenery. The sand, gravel, and drift accumulations of every kind are common to every country where waters flow or valleys exist. They cover the great straths of Scotland, the low steppes of Russia, the lofty gorges of the Himalaya, the desert wastes of Africa, and the elevated plateaux of North and South America. Among the Rocky Mountains they are of the most varied character, and are spread over extensive areas in those sterile regions, high up among the sources of the great American rivers. Wherever a stream falls into another stream, a stream into a lake, a lake into a river, or a river into the sea, bars, gravelly shoals, and deltas are found to exist, or to be in the act of formation. Accumulations of this class, therefore, are to be regarded as of various periods, as they are evidently the results of causes of continual operation, ordinary as well as extraordinary. Many of such phenomena, however, are as clearly the indication of a state of things which no longer exists. Whether by a subsidence in the sea-bottom, or an elevation of the land, they are now raised far above the influence of the element within which they were collected, and to whose abrading powers they owe their laminated structure. Such, in particular, are those regular-shaped terraces as well as detached hillocks of sand and gravel, several hundred feet in depth, so common in the straths of Scotland and valleys of Switzerland, through which arms of the sea or of great inland lakes once penetrated, and over whose shores and bottoms the debris of the mountains gradually accumulated. “The Sea Margins,” the work of the accomplished Robert Chambers, contains a minute and interesting detail of these facts, gleaned from varied sources of reading and most extensive personal observation, and clearly warranting the inference that the sea at no very remote period covered vast districts of country from which it has now receded.