OF THE CABBONlFKROtJS STRATA. 189 



boniferous limestone seen in the vicinity. Tlie beds of stone 

 vary in thickness from the twentieth part of an inch to six 

 inches and more. Upon their upper surface is a meandering 

 trail of about two-tenths of an inch in breadth* This is most 

 frequently found in relief, but sometimes in intaglio. Fig. 1^ 

 plate Ij drawn on the natural scale, will give an idea of the 

 nature of the majority of these trails, which cross each other 

 several times and run to a considerable length. The hollow 

 trails are deepest in their middle, and have their margins 

 raised by a slightly elevated ridge of sand. 



Besides the trail last described there are two others, namely, 

 a broad one of half an inch wide, and generally straighter, 

 but not so long in its course as the smaller ones ; and a double 

 trail, having markings a little less in size than the first de- 

 scribed, and about one inch apart, generally running in nearly 

 straight or slightly curved lines. These last somewhat resem-* 

 ble the track of small crab on the present sand beaches. 



Some of the American tracks are so much like those at 

 Hutton Roof that a description of the one would nearly 

 suffice for the other. 



At p. 256 of the Proceedings of the American Association 

 for the advancement of Science, Professor Hall, in describing 

 the tracks found on thin layers of sandstone^ alternating with 

 skaly beds, in the lower part of the Clinton group in the 

 central part of New York, which he considers to have been 

 made when the bed was exposed above water, or beneath 

 shallow water only, proceeds as follows : — ** The general cha- 

 racter of the trails here noticed is that of a meandering furrow, 

 more deeply depressed at the two sides, elevated at the cen- 

 tre, and margined by a slightly elevated ridge of sand which 

 appears to have been pushed outward in the progress of the 

 animal. Others of them are a simple furrow with the deep- 

 est depression in the centre ; while others are fimbriated or 

 ciliated along their whole extent; proving that they were 

 produced by several distinct species of animals. In their 



