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GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



Lower Carboniferous <j 



^ Lower Limestones, 

 j Calciferous Sandstone ( Cementstone Group. 

 Series (. Cornstone Group. 



The arrangement of the Carboniferous rocks of Ireland is on the whole similar to 

 that in England, the marine limestones of the Carboniferous Limestone series being very 

 largely developed and covering a great extent of country, from which the overlying Coal 

 Measures have been mostly swept away by denudation, and now exist only as small 

 isolated patches, whose horizon is supposed to be that of the Lower or Gannister beds of 

 England. Mr. Hull is, however, of opinion that the coal-bearing strata of Ballycastle in 

 the north of Ireland belong to the same geological horizon as the Edge Coal series of 

 Scotland, namely, to that of the Carboniferous Limestone. Below the Carboniferous 

 Limestone there is also found in the south-western parts of Ireland an extensive series of 

 strata consisting of grits and slaty rocks, for the most part very unfossiliferous, though in 

 some places they contain marine fossils of well-known Carboniferous types, e.g. Spirifer 

 cuspidatus, Bhynchonella pleurodon, &c. This series, known as the "Carboniferous 

 Slates," is probably contemporaneous with the Calciferous Sandstones of Scotland, 

 although formed under different conditions. Like the last-named set of rocks, the 

 Carboniferous Slates rest conformably on the Upper Old Red Sandstone, the fossiliferous 

 beds of Kiltorcan being evidently equivalent to the Holoptyc/iius-he&vmg beds of Dura Den 

 and other places in Scotland already referred to. 



Remains of Fishes occur throughout the Carboniferous series, frequently occurring 

 only as detached teeth, bones, spines, and scales ; frequently also, and especially in certain 

 localities, entire specimens of the smaller forms are met with. They occur usually in the 

 shales, ironstones, and limestones, very rarely in the sandstones, and in the case of 

 the ironstones they frequently form the nuclei of the concretions known as " nodules " 

 or " ironstone balls." Entire specimens are usually so much crushed and flattened, the 

 bones of their heads so broken and squeezed together, as to render the investigation 

 of their cranial structure a matter of extreme difficulty ; indeed, in too many cases the 

 crushed heads cleave more or less through the middle, so as to present nothing more to 

 the eye than a confused paste-like bony mass, which is utterly unreadable. For 

 structural investigations the heads contained in ironstone nodules are the best, as here the 

 matrix seems to have acquired a consistency sufficiently hard and unyielding to preserve 

 the contour of the bones in tolerable condition before the operation of those immense 

 crushing agencies, which in other cases have left the structural features undecipherable or 

 nearly so. The comparison of species from different localities and horizons is also much 

 interfered with from the different conditions of preservation so often displayed by 



