132 



THE GEOLOGIST. 



of fossil tracks with some good results, is to be found iu Prof. Em- 

 mons's ' American Geology,' part vi., 1857, chap, xvi., p. 135, etc. 

 Eeferring to the fossil tracks found so abundantly in the sandstone 

 of the Connecticut Yalley, he says : — " In the progress of discovery 

 other imprints have come to light, diifering in every respect from the 

 preceding. Those in the first instance were regarded as fossil Ne- 

 reites, 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- 

 er 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 addi- 

 tion to these, there are many others which must be due to water- 

 insects, or their larv88. We may easily convince ourselves of the 

 possibility of the preservation of footprints, or the trails of the bodies 

 of larvae, 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 diff'erent patterns, according to tlie 

 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 pheno- 

 mena of a similar kind, I propose to illus- 

 trate their characters by the annexed figures 

 of some of the more common form of trails 

 wliich 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 larvse of two different species 

 of dipterous insects. It is, however, only 

 of the larger that I can speak with cer- 

 tainty ; 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 

 tlie larva entered the mud. Frequently 

 the larger trail terminates in a hole in 

 the mud also. Fig. 106 (hg. 4) is copied 

 from another pattern, having lateral 

 fringes. This resembles very closely the 

 iniprints wliich have been referred to Ne- 

 reites. Upon this surface, also, the im- 

 l)rcssious of rain-drops are perfectly pre- 

 served. 



" An equally interesting kind of trail 

 IS exhibited in the margin (fio-. 107) 

 which was probably made by a'' water^ ^ ^ ^""'i""^)- 

 insect, or one having legs (hg;5). The first (fig. 105) were made by 



Fig. 3 (105, Emmons). 



