OF THE CARBONIFEROUS STRATA. 



193 



extensively worked. For some years T have been of opinion 

 that these deep impressions were the casts of a bivalve shell, 

 and the shallow ones its trail in the sand, when the latter 

 was in a soft state. 



During the cutting '^f the Manchester and Huddersfield 

 Railway through the lower flagstones at Scout Mill, between 

 Staleybridge and Mossley, I found a specimen which gave me 

 decisive proof that I was not mistaken in my former opinion. 

 In this specimen, figured at plate II. fig. 1, drawn on a scale 

 of one-seventh the natural size, the casts of several shells, 

 apparently of the genus modiola, with their trails, are dis- 

 tinctly seen. The curve which the animal made in its track 

 much resembles that of the psammobia solidula on the soft 

 mud of our present coasts, and presents a very marked dif- 

 ference to the meandering trails of the littorina and some 

 other univalves, to which the most common trails on the 

 flags of Hutton Roof, if they are not worm marks, must be 

 referred. 



The whole appearance of the trail leads me to believe that 

 it was Ibrmed under shallow water, just as we now see indivi- 

 duals of the geneva psammobia and naticof nake trails upon 

 the mud at the bottom of the pools on the sea shore. And in 

 confirmation of this view I may add, that the thin beds of 

 clay separating the deposits of flags shew no evidence of 

 desiccation by cracks in them, which they would have done if 

 they had been exposed to the sun's rays. 



In a paper by me, printed in vol. viii. of the Society's 

 Memoirs, at p. 171 is figured the cast of a small annelid of 

 nearly the shape of the letter S, about an inch long and a 

 line in breadth. It is merely a cast of the animal itself with- 

 out any trail, in a bed of fine sandstone, and found by me in 

 the lower flags near Todmorden. 



I shall now proceed to make some observations on a spiral 

 fossil shell frequently found in the Lancashire coal field, and 

 long known by the name of microconchus carbonarius, Mr. 



2c 



