106 S. P oivers — Gastropod Trails in Sandstones. 



pound type while all other surfaces within a few inches 

 both above and below in the section show simple trails is 

 difficult to account for. 



The frequency and curvature of the trails are best 

 understood by referring to the illustration. One slab 

 shows 26 distinct trails in 56 sq. inches or one trail to 2 sq. 

 inches. The trails bend sharply, cross, and occasionally 

 combine, but there is no indication that the animals had 

 any common trail or that they crawled over a former 



Fig. 3. — Short portions of two very well preserved trails showing the 

 lobate character of the sand which was pushed aside during the advance of 

 the animal. One-fourth less than natural size. 



trail except by accident. The frequent turns in the trails 

 indicate that the animals were not in the habit of pro- 

 gressing in a straight line and therefore it is inferred 

 that their power of vision was extremely limited. Be- 

 cause there is no indication of common centers from 

 which tracks lead and because the tracks end suddenly 

 it is evident that the animals burrowed into the sand or 

 mud and that the wet mud concealed the places where 

 they disappeared and reappeared. 



Professor Raymond has examined trails on beaches 

 near Boston with reference to the origin of these tracks 

 and he finds that the common gastropod Littorina prac- 

 tically duplicates them except that the convex ridges 

 along center are not so steep as in some of the fossil 



