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THE GEOLOGIST. 
The eastern and southern slopes of the hill are gentle, but its more abrupt 
north-western face forms a bold feature in the landscape. 
The rocks of which the core of the hill and this steep slope are formed 
belong to the Silurian series, and consist of grey and bluish hard grits and 
sandstones, interstratified with coarse conglomerates and fine flaggy and slaty 
shales. 
The eastern and southern slopes of the hill are formed of the Old Red Sand- 
stone, which is represented here by whitish conglomeratic beds, dipping at low 
angles from the higher Silurian ground towards and underneath the overlying 
limestones of the surrounding plain. One of the most interesting points in the 
structure of the hill was stated to be the disappearance of the Old Red Sand- 
stone along its W, or steep flank, in consequence of the occurrence of a fault 
rumiing along the base of the high ground at that side, nearly parallel to the 
direction of its crest. By this fault a displacement of the rocks was caused, 
amounting to more than 800 feet. This fracture does not seem to have been 
the cause of the occurrence of a hill here, for as the Old Red Sandstone shows 
a tendency to curve round the N. end of the hill, and actually does so at the 
S., it seems likely that the hill was originally formed by an anticlinal, the axis 
of which was arched at this place, and afterwards very obliquely crossed by 
the fracture, along which the beds to the W. received an opposite or downward 
curvature. Along the W. side of this fracture the limestone is let down so as 
to come into juxtaposition with the Silurian rocks, and here, as is frequently 
Diagrammatic Cross-section of the Hill of Knockshigowna. 
A, Fault ; B, Silurian ; c. Old red sandstone ; D, Carboniferous limestone. 
the case along lines of fracture in limestone beds, the rock is converted in 
places into a (yellowish) crystalline dolomite. In other places where the 
sequence is undisturbed, the lowest beds of the limestone series immediately 
overlying the Old Red Sandstone -are found to consist of the usual dark 
earthy limestones, and cleaved, olive, calcareous shales, both being highly 
fossiliferous. 
A peculiar group of red calcareous beds occurs in the Silurian rocks, close to 
the unconformable boundary of the Old Red, and they may be traced along 
their strike passing gradually from the ordinary bluish grey into a deep red 
colour just before they disappear beneath the Old Red Sandstone ; a circum- 
stance which is in other places very common along the unconformable boundary 
between this Old Red Sandstone and the adjacent Silurian, particularly when 
the latter is composed of shaly beds. 
Fossils. — These calcareous red rocks do not appear to contain fossils, but in 
the vicinity of a remarkable band of conglomerates in the Silurian, near Fairy- 
mount-gate-lodge, and also in the conglomerate itself, and in the neighbouring 
shaly flags, fossils were stated to have been found by the author and W. H. 
Baily, Esq., F.G.S., by the latter of whom the following list was prepared : — 
