292 



Ichthyolites are generally in a highly bituminous shale, 

 sometimes forming the roof, and at other times the floor, 

 of the Coal seam ; while the fossil plants occur in the 

 argillaceous shales and sandstones, which occupy the same 

 situation, but appear destitute of the former substance. 

 Can the presence of bituminous matter in the one instance, 

 and its absence in the other, be owing in any degree to 

 the decomposition of animal substances ? which has been 

 conjectured by some writers as affording a probable ex- 

 planation of the difference which they present in miner- 

 alogical analysis. 



The different seams of Coal, even in the same pit, will 

 not always yield the same remains. At Middleton, there 

 are three seams, known as the Fish Coal, Yard Coal, 

 and Main Coal. In the roofing shale of each of these 

 seams fish remains occur, but in the first more especially ; 

 hence the colliers have designated it the Fish Coal, and Mr. 

 Teale the Ichthyophorous shale. In the Main Coal shale, 

 we find a much smaller number of fish exuviae, but they 

 are of a peculiar character and of greater magnitude, such 

 as large vertebrse and dorsal rays or spines, &c., of shark- 

 like fishes ; while the Yard Coal is still more deficient, and 

 contains only a few small teeth of Holoptychius and Ctenop- 

 tychius. 



" The manner," observes Mr. Williamson, " in which 

 Ichthyolites are associated with other remains in different 

 localities is well worthy of attention. At Burdiehouse, 

 they occur in the midst of Unios, Cyprides, and Micro- 

 conchus Carbonarius ; at Colebrook Dale, with species of 

 Orbicula, Trochus, Nautilus, Orthoceras, and Conularia ; 

 in the Lower Measures of Lancashire, in beds nearly 

 associated with those, containing Goniatites Listeri, and 

 Pecten Papyraceus ; in the Higher Measures of Lanca- 

 shire and in Yorkshire, with Unionidae and Entomostraca ; 



