In journeying up the Delaware and approaching Trenton, we have passed through a region of most interesting geological development. All along are evidences of the deposit of the drift from above, which is popularly known as the "Trenton gravel." The Delaware flows southeast from the Kittatinny Water Gap to Bordentown, and then, impinging against the cretaceous stratified rocks of New Jersey, abruptly turns around a right-angled bend and goes off southwestward towards Philadelphia. The river has thus deposited the Trenton gravels, composed of the drift of most of the geological formations in its upper waters, throughout its course, on the Pennsylvania side from Trenton down below Philadelphia. This deposit is fifty feet deep on the river bank in Philadelphia, and underlies the river bed for nearly a hundred feet in depth. At Bristol the deposit stretches two miles back from the river, and at Trenton it is almost universal. The material, which in the lower reaches is generally fine, grows coarser as the river is ascended, until at Trenton immense boulders are often found imbedded. We are told by geologists that at the time of the great flood in the river which deposited the gravel, the lower part of Philadelphia, the whole of Bristol and Penn's Neck and almost all Trenton were under water. The gravel has disclosed bones of Arctic animals--walrus, reindeer and mastodon--and also traces of ancient mankind. The latter have been found at Trenton and on Neshaminy Creek, indicating the presence of a race of men said to have lived about seven thousand years ago. The river has also made immense clay deposits all along, which was done at a time when the water flowed at a level more than a hundred feet higher than now.