PROCEEDIXGS OF GEOLOGICAL SOCIETIES. 805 
creation and of occasional migrations, — tlie conditions of contemporaneity, — tlie 
relations of geographic and ei)oclial centres of life, — the laws of recurrence of 
animal forms, or their reappearance in new epochs, and of the disappearance of 
ftiuna', — and lastly the^ points of similarity and of dissimilarity between the 
palajozoic rocks of Wales and Xew York wore, in the concluding portion of the 
memoir, lully dwelt upon. 
June 9, 185S. — 1. " On Jointings, and on the Dolomites near Cork." By Pro- 
fessor Harkness, P.R.S., F.G.S. 
The strata in the neighbourhood of Cork consist of Devonian rocks, and the 
lower portion of the Carbonifei-ous series. In the former a regular system of 
north and south joints occur, cutting tlirough the strata at nearly right angles to 
their strike. The carboniferous rocks are also intersected by joints having a 
similar direction; but in these latter rocks other joints occur, one system of which 
approaches to the horizontal, and the other is inclined sometimes towards the 
east, at other times towards the west. This threefold system of jointings, which 
make their appearance in the carboniferous rocks, is not equally prevalent in all 
the members of this series. 
The limestones in which they occur in the greatest perfection are such as have 
the greatest amount of carbonate of lime, and are of the pm-est characrter. 
In some siliceous limestones, which are associated with the more perfectly jointed 
rocks, the series of jointing is confined to such as prevail in the Devonian strata, 
these having only the north and south system of divisional planes. Ke.specting 
the north and south series of joints, the author is disposed to regard them as 
resulting from pressure, caused by the movements which have given to the 
strata in the south of Ireland an arrangement in the form of rolls, having an east 
and west strike, — a course at right angles to the direction of the principal joints. 
In connexion with these north and south joints, both in the limestones of the 
carboniferous series and also in the underlying carboniferous slates, the author has 
noticed distortions of fossils, and this distortion consists of an elongation between 
the series of joints, the fossils being pulled as it were out towards the sides of 
these planes, or at right angles to the strike of the joints. 
Prof. Ilanghton has already noticed the elongation of the fossils in the direction 
of the strike of cleavage, a mode of elongation at variance with that described by 
Prof. Phillips and the late Mr. D. Sharpe. 
As this direction (of distortion), however, occurs among strata in the north of 
Ireland devoid of cleavage, the author is disposed to regard it as resulting rather 
from jointing than from cleavage, and he regards it as evidence that pressure has 
exerted considerable inrtuence in producing joints. Concerning the other two 
systems of joints, which are peculiar to the purer limestone, these have a dissposition 
to split the masses of limestone into rhomboids ; and these divisional planes, the 
author considers, result from the same cause as the principal joints ; but, owing to 
the pure state of the limestone, lines of division akin to ndntral claivtije. have 
intersected these strata, and given to them their complex series of jointings. 
Dolomites also occur in the limestones of the district around Cork. Tliey 
usually are met with in a dyke-like form, and in general are found conforming to 
the strike of the perpendicular north and south joints, or, in other words, intersect- 
ing the strata at right angles. 
In some instances, however, they have an east and v.-est course, and are found 
associated, in this condition, with the siliceous limestones which possess only the 
principal system of joints. 
These dolomites, from their mode of occurrence, have had their origin subsequent 
to the production of the joints, and are often found thinner belov/ than above. 
From the circumstances of their occurrence, the author is disposed to regard them 
as metamorphosed ordinary limestones, and the mctamorphic action he is disposed 
to attribute to sea-water, which, containing sulphate of magnesia, has found access, 
by means of the joints, into the limestone masses; and this at an elevated temperature, 
combined with j)ressure, has produced these changes, by the double decomposition 
of sulphate of magnesia and carbonate of Time, and, by this means, given rise to 
the production of the dolomites occurring in this neighbourhood. 
