Page:The Geologist, volume 5.djvu/156

132 of fossil tracks with some good results, is to be found in Prof. Emmons's 'American Geology,' part vi., 1857, chap, xvi., p. 135, etc. Referring to the fossil tracks found so abundantly in the sandstone of the Connecticut Valley, he says:—"In the progress of discovery other imprints have come to light, differing in every respect from the preceding. Those in the first instance were regarded as fossil Nereites, Myrianthes, etc., or Annelids, whose surfaces, or exterior, possessed a sufficient consistency to form an imprint upon a yielding surface. Most of these markings, however, are now referred to foot- or body-marks of Crustacea or Mollusca, which have been made in a manner similar to the trails of certain shell-fish, as they move over a soft bottom. Such trails are preserved upon the rocks; but in addition to these, there are many others which must be due to water-insects, or their larvæ. We may easily convince ourselves of the possibility of the preservation of footprints, or the trails of the bodies of larvæ, by the inspection of a pool of water which has stood a few days after a shower of rain. These pools, while drying, will leave frequently a smooth, glossy surface of indurated clay or mud, which will be marked by innumerable tortuous lines of different patterns, according to the character of the body and feet possessed by the animal which has travelled over this smooth impressible surface.

"As these recent trails are instructive as well as useful in explaining ancient phenomena of a similar kind, I propose to illustrate their characters by the annexed figures of some of the more common form of trails which may be seen by the margins of drying pools of water during the summer season. Fig. 105 (fig. 3) is a copy of the imprints made by the larvæ of two different species of dipterous insects. It is, however, only of the larger that I can speak with certainty; for I have found in this trail, or by it, the dead larva. The darker spots which terminate the finer trail mark the places where the larva entered the mud. Frequently the larger trail terminates in a hole in the mud also. Fig. 106 (fig. 4) is copied from another pattern, having lateral fringes. This resembles very closely the imprints which have been referred to Nereites. Upon this surface, also, the impressions of rain-drops are perfectly preserved.

"An equally interesting kind of trail is exhibited in the margin (fig. 107), which was probably made by a water-insect, or one having legs (fig. 5). The first (fig. 105) were made by