DAVIS : DISTRIBUTION OF FOSSIL FISHES. 
229 
The millstone grit rocks merge gradually and without any- 
distinct or arbitrary dividing line into the coal measures. The 
thick-bedded, often coarse, grit rocks with thick intermediate beds 
of shales give place to finer sandstones and shales, with occasional 
coal seams in the lower coal measures, and these again to the more 
rapidly alternating shale and sandstone, and frequently recurring 
coals of the middle coal measures, 
The fossil fishes in the coal measures of Yorkshire hitherto 
discovered, have been principally from two or three localities. 
In almost every instance where those remains have been found 
they are obtained from the shale immediately above a coal bed, and 
they usually present the same features throughout the whole series. 
The genera of fish found in the lower coal measures are also found 
in those higher in the series, but there is not always the same 
proportion of individuals of any given genus in the same beds. 
Some genera are of frequent occurrence in the higher beds, whilst in 
the lower, though still present, they are in much diminished numbers. 
The fishes are not often found over large areas, even when a 
seam of coal, above which they have been found to occur in tolerable 
abundance in one locality, extends persistently over a large area, it 
does not follow that the fossil fish will be uniformly distributed 
over that area. In most instances, on the contrary, the fishes are 
discovered in certain districts, whilst in others the same bed, on the 
same horizon, is unproductive. It is worthy of remark, that 
where fish are found above any given bed of coal, though the situa- 
tions may be widely separated, there is a close relationship between 
the fish of the several localities, for example, the Halifax Hard 
Bed Coal in the neighbourhood of the town from which it derives 
its name has yielded remains of ]\Iegalichthys, Ccelacanthus, Acan- 
thodes, and others. At Baildon, near Leeds, where fish-remains 
have also been found above this coal, they are generically identical. 
The specimen which served as the type for Prof. Aqassiz's descrip- 
tion of the genus Ccelacanthus was obtained from a large nodular 
mass locally known as a ' baum-pot ' above the hard bed coal at 
Halifax. Fish-remains in the Halifax beds are not common, and 
