THE LOWER CARBONIFEROUS BEDS OF HOOK. 
151 
&c., leads us to conjecture that the depth of the water was moderate, 
probably not exceeding 70 feet. 
4 . DOLOMITE BEDS. 
The limestone beds of the Hook peninsula are divided into two 
nearly equal portions by a very remarkable band of dolomite, quite 
unfossiliferous, or presenting only traces of nearly obliterated fossils, 
with some obscure remains, which are either casts of fucoids or of 
annelid burrows. I estimate the thickness of this belt of magnesian 
limestone at 385 feet; it is conformable, both above and below, to 
the flaggy limestone which preceded and followed it. I think it 
probable that this band of dolomite corresponds with the lower 
magnesian band described by Mr. "Wyley in his account of the lower 
Carboniferous limestone of Kilkenny and Carlow.*' It resembles it 
in physical characters, in the absence of fossils, although interposed 
between limestone beds remarkably fossiliferous; and it occupies 
the same geological horizon,—Mr. Wyley’s dolomite lying 1100 feet 
above the base of the lower Carboniferous limestone, and the dolo¬ 
mite of Hook being about 900 feet above the uppermost plant beds 
of the Yellow Sandstone series. They are also comparable in point 
of thickness,- the dolomite of Kilkenny being 200 feet thick, and the 
Hook dolomite 380 feet. 
5. NEWER LIMESTONE BEDS. 
The beds of limestone which rest conformably on the dolomite, 
and extend southwards to Hook Lighthouse, are 981 feet thick; 
they resemble closely the upper beds which underly the dolomite, 
and are composed of flaggy limestone, with alternations of black 
calcareous shale, the unequal weathering of which gives rise to a 
fine development of beautiful fossils on the exposed surface of the 
thin-bedded limestones. A remarkable series of limestones, contain¬ 
ing fish teeth and spines of large size, of the genera Psammodus and 
Ctenacanthus, accompanied by myriads of Orthis filiaria , rests upon 
the dolomite, and occasional fine specimens are found throughout 
the entire series; the large size of the fish teeth, and their perfect 
preservation, coupled with other circumstances, lead us to believe 
that the water, which had been gradually deepening from the period 
* Geol. Soc. Dub. Journal, vol. vi., p. 109. 
