THE EXISTENCE OF FOSSILS IN THE LIMESTONE OF CULDAFF. 163 
The Society met on the 14th of May, 1856, on which occasion the 
following Paper was read. 
ON THE PROBABLE EXISTENCE OF FOSSILS IN THE LIMESTONE OF 
CULDAFF, COUNTY OF DONEGAL. BY PATRICK GANLY. 
From the data supplied by the publication of Mr. Griffith’s Geolo¬ 
gical Map, it may be easily shown that the slate group composing 
the valley of the Foyle is the newest portion of the primary 
series in the north of Ireland; but it would appear from observation, 
that, although connected with our oldest sedimentary deposits by a 
conformable sequence, these strata agree in lithological aspect rather 
with the base of the Silurian System, as in Wicklow and Wexford, 
than with the more prevailing rocks of the primary series in Galway, 
Mayo, and Donegal, and generally consist of black, shining clay-slate, 
frequently alternating with white quartzite, and occasionally with 
gray crystalline and compact limestone. 
The limestone, however, is chiefly confined to the base of the 
group, and attains its greatest development in the neighbourhood 
of CuldafF, where, though much disturbed by extensive protrusions 
of greenstone, it presents a succession of beds fully four hundred 
feet in thickness, remarkable for the greater part in containing an 
abundance of symmetrical concretions disseminated through the rock, 
in the manner of fossils, amongst more recent strata. 
The concretions are usually found isolated, and of different 
forms, but those of most frequent occurrence are somewhat semi- 
globular, and vary in size from two inches to a foot in their greatest 
dimension. On the principal fracture they always exhibit a radi¬ 
ated structure, and after ,more detailed examination appear to be 
composed of a mass of truncated pyramids, terminating on the base 
or outer surface in a network of irregular polygons, which seldom 
exceed one-third of an inch in diameter. 
Whether the specimens be compact or crystalline, their internal 
structure is still the same; and in relation to the strata in which 
they occur, it is not observable that the sedimentary lines of the 
bedding pass in any case through the enclosed concretions, nor that 
the radiating jointage of the latter ever extends into the surround¬ 
ing rock; so that, taken as integral masses, these concretions would 
seem to be of anterior origin to the beds in which they are found, 
