Page:The Geologist, volume 5.djvu/157

Rh an apodous larva. This imprint (fig. 107) was made upon an impressible surface, but sufficiently indurated to preserve the form and character of the trail. This trail, however, is gradually changed into one having the form exhibited in fig. 108 (fig. 6). This fact is important, and should be remembered. The change in this instance is due to the change in the consistence of the mud itself. In the last figure it is copied from that part of the trail which was made when the water still stood over it, and when it was so liquid as to flow and fill up, in part, the imprint. The two patterns are so different that, if they were apart, they would very naturally be attributed to two quite different animals.

"Imprints upon the Taconic slates in Maine and New York do not differ materially from the foregoing. So, also, those upon shales belonging to the Ontario division, near Utica, which I was the first to point out, and which are figured in Mr. Hall's second volume of Palæontology, appear to have been made by water-insects; at least, they do not differ very much, in character and form, from many which we may find in drying pools after our summer showers.

"Fig. 108 is not very unlike a figure which I gave several years ago in my 'Report of the Geology of New York,' and which were made upon the green slates belonging to the Taconic system in Maine, and slates, too, which are among the oldest sediments in the world.

"If the foregoing remarks and observations are true, it proves that the soft fragile larvæ of insects existed in the earliest periods, or at the time when the oldest sediments were deposited."

Going on to speak of the fossil tracks and trails in the Connecticut sandstones at Turner's Falls, Professor Emmons expresses a belief that the tracked surfaces formed a border around and outside the main body of the sediment, and were due to the overflow of rivers and ponds after heavy rain-falls. "This view of the subject," he says, "is sustained by what takes place in every great freshet in the rivers of the Southern States. Here the large rivers and their tributaries, such as the Oronoko, Dan, and Cape Fear, overflow their banks, and spread over the meadows or low ground, upon which a sediment two or three inches thick is thrown down. The river, on subsiding, leaves the deposit to dry gradually; and, in the meantime, it will be tracked by insects, worms, frogs, lizards, rats, and birds, all of which will