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lines at rifjht angles to the centre one ; and these seem to have had 

 their origin in the rings of the body of the annelid. 



The nature of the tracks as they occur in the lower flags, which 

 are dark-coloured, is somewhat different. On the upper surfaces of 

 these they appear also in the form of sinuous fui-rows, about the 

 same width as the more perfect tracks of the higher flags. Here, 

 however, they rarely present crenations, being regular on their 

 margin, and having, in many instances, the impression of the ventral 

 arch distinct. 



The various appearances of the tracks, and the nature of the strata 

 with which these are associated, furnish some important information 

 concerning the conditions which obtained when this portion of the 

 Millstone Grit series was being deposited. The tracks, from their 

 various states of perfection, indicate that, in some instances, the mud 

 which now constitutes these flags had been in different states, as 

 concerns consolidation, at the time when it was traversed by these 

 animals. It sometimes appears to have been in a state so saturated 

 with water that it assumed a pasty condition, partly flowing in upon 

 the tracks after these had impressed its surface, and obliterating the 

 markings of the cirri. At other times it seems to have been suffi- 

 ciently consolidated to afford the requisite conditions for more perfect 

 tracks, as in the case of the higher greenish-gray flags. 



The animals which impressed these Irish flags appear to have 

 been widely different from those which have burrowed in the deposits 

 which now form the flags of the lower portion of the Lancashire coal- 

 field, since, in these latter, neither the entrance into the burrows nor 

 the burrows themselves, equal the annelid burrows of the flagstone of 

 Clare ; the former having only a diameter of one-fifth of an inch, and 

 being apparently round, while the latter are half an inch in breadth, 

 and have their form flattened longitudinally, which gives to them, on 

 transverse section, the lenticular shape already referred to. From 

 their crenulated margins, which would indicate that the cirri were 

 more perfectly developed in the annelids to which we owe these 

 tracks, it would seem that they are more nearly allied to those which 

 have impressed the strata of the older formations, than to such as 

 have left their markings on the English carboniferous deposits ; and 

 if we adopt the general appellation of Sir Roderick Murchison, they 

 might be considered as the carboniferous type of the ancient A'erites, 

 and be designated Nerites carbonarius. 



2 A 2 



