Page:Popular Science Monthly Volume 55.djvu/346

330 of tide water, and almost every essay differs in more or less degree from its fellows in the matter of the gravel's age as a well-defined deposit. Its origin no one can question, nor the agencies by which it was brought to where we now find it. Ice and water did the work, nor have they ceased entirely to add to the bulk transported in strictly glacial times—perhaps it were better to say in superlatively glacial time, as the river even now can be positively glacial upon occasion, as Fig. 2 demonstrates. The main channel has often been completely blocked with ice and the water forced into new directions and spread over the lowlands or flats, which it denudes of its surface soil, and once within recent years the stream found an old channel, deepened it, and for a time threatened to leave a flourishing riverside town an inland one. Ice accumulated in this way year after year must necessarily affect the river's banks, and yet the extent of "damage" is trifling usually, in comparison with that of the water, particularly when agitated by passing steamboats or violent winds; and now, too, the ice of our present winters does not transport coarse pebbles to any significant extent. I am convinced of this since the examination I gave acres of ice, when the river was gorged with it, some years ago. It was possible to walk for miles over the ice, as shown in Fig. 2, and to see it under exceedingly favorable circumstances, and a most careful search failed to reveal a stone larger than a pigeon's egg incased in this ice, which was all gently floated from far up the stream and stranded here; and where piled up upon the shores it usually remains until melted, and really acts as armor plate, protecting the ground from abrasion when the floods incident to the "break-up" prevail. Such are the present-day considerations, and they have a direct bearing upon the question of man's antiquity here because, first, the river valley has not varied for huidreds of years, except in becoming wider, the low shores receding, and the stream becoming broader and more shallow. In earliest Indian times the river was subject to freshets and ice gorges as now, but never did the water become so dammed up as to overflow the broad plateaus, areas of glacial gravel, that at the close of the Glacial period were within the boundary of the river. The Delaware was a very different stream then—crescendo for thousands of years, and diminuendo for thousands since—until now it barely hints at what once was. But not even in the height of its glacial activity was the climate so severe that the waters contained no fish, nor the forests of the high surrounding hills harbored no game. Never was it as bleak as the arctic region of to-day, and as man maintains a footing there, why should he not have done so here, where life was ever more easily sustained? True: but did he live here in glacial time?