192 



ON SOME TRAILS AND HOLES FOUND IN EOCKS 



drawn on tlie natural scale, appear to shew that they were 

 formed by an animal of Cuvier's division of annelides of 

 the second family, or dorsibranchiata, where the external 

 breathing organs or gills, often resembling beautiful feathery 

 tufts, are attached in pairs, either to every segment of the 

 body, or to a certain number of middle segments. The 

 organs often display the most elegant varieties of form and 

 the richest colours. To this order belong the majority of 

 the present marine annelids, and, among the rest, the com- 

 mon lug worm, arenicola piscatprium. It is to this last 

 named annelid, or one nearly allied to it, that I am inclined 

 to attribute the holes above described. The fossil holes are 

 smaller than the recent ones. With this exception, the 

 only difference that I can detect betwixt the fossil holes and 

 those at present found on our sandy shores is, that there 

 are no traces of the coils of sand at the vent end of the 

 hole, which so generally accompany those of the lug worm 

 at the present day. These may have been formed under 

 water, and afterwards washed away, but certainly I have not 

 yet been able to detect any near the fossil specimens. The 

 animal which inhabited the hole appears to have drawn in 

 the water and sand by one opening, and ejected them from 

 the other. 



For a provisional name I have designated the animal which 

 made the holes arenicola carbonarius. 



Upon the surfaces of some of the finer beds of the lower 

 flag deposit are often seen numerous depressions of a more 

 elongated and bent form than those last described as occurring 

 in the upper flags. Some of them are about an inch in 

 length and a quarter of an inch in breadth. Near to these 

 are sometimes seen traces of a furrow or trail, more or less 

 distinct according to the nature of the flag, whether it is fine 

 and smooth-faced or otherwise. They are seen in the flags of 

 Edgeworth near Bolton, Fo Edge near Bury, Shawforth 

 near Rochdale, and other places where the lower flags are 



