TRANSACTIONS OF THE SECTIONS. 69 
rain; in some instances, however, oblong impressions make their appearance, and 
they are the results of heavy drifting rain, All the physical conditions on these 
ancient shores are such as we find under fayourable circumstances on the sandy and 
muddy coast of our present seas. 
On a Model illustrative of Slaty Cleavage. 
By the Rev. Professor Haucuton, M.A. M.R.LA. 
This model was intended to illustrate Mr. Haughton’s views respecting the distor- 
tion of fossils by cleavage. It was made of zinc, and represented one-eighth part of 
the ellipsoid of compression. A moveable zinc quadrant might be placed in different 
positions in the model, and thus show the manner in which the line of greatest elonga- 
tion of the fossils shifted with the intersection of cleavage and bedding. 
Mr. Haughton stated that in all the rocks he had hitherto examined, the ellipsoid 
of compression was very nearly oblate, with its short axis perpendicular to the planes 
of cleavage. —_—_—_ 
On Fossil Stems allied to Stigmaria, recently obtained from the Upper Beds 
of the Old Red Sandstone of Hook Point, Co. Wexford. By the Rev. 
Professor Haucuton, M.A., MLR.LA. 
It is well known to geologists that many plants of the genera Stigmaria, Lepido- 
dendron, Knorria, Sigillaria, &c., have recently been found on this geological horizon 
in Donegal, Mayo, Kilkenny, Cork, and Wexford. 
The specimens found at Hook Point are generally in very bad preservation. Those 
exhibited by Professor Haughton showed the structure of the stem well-preserved. 
There must have been a central bundle of vascular tissue, more or less woody; a 
_ hollow stem, and a thick bark ; the latter being connected with the central vascular 
column by oblique spinous bundles analogous to the medullary rays of Calamites, 
In the specimens exhibited by Prof. Haughton, the central vascular column was 
represented by a hollow tube filled with coaly matter and surrounded by the sandstone 
cast of the hollow stem, outside of which again appeared the carbonaceous remains 
of the bark of the stem, with the spinous processes on its inner surface. On the 
whole he considered these obscure remains of the earliest vegetation of Ireland to be 
allied to Stigmaria more closely than to any other fossil genus, and he believed that 
there were some peculiarities in these plants which would amply repay a careful study. 
Accompanying the plant beds at Hook, was a thin bed of anthracitic coal, about 
2 inches thick, the stems being found in the soft sandstone beds both above and below 
the coal seam. The stems were sometimes 2 feet long, and always terminated 
abruptly in the rock. 
In conclusion, ‘Prof. Haughton stated that geologists present at the Meeting would 
be able to form an excellent idea of the yellow sandstone flora by visiting the Museum 
of the Geological Survey, Royal Dublin Society, and Trinity College, all of which 
contained fine specimens of these plant remains. 
On the Existence of Forces capable of changing the Sea-level during different 
Geological Epochs. By Professor Hennessy, M.RIA. 
If, in assuming its present state from an anterior condition of entire fluidity, the 
matter composing the crust of the earth underwent no change of volume, the direction 
of gravity at the earth’s surface would remain unaltered, and consequently the general 
figure of the liquid coating of our planet. If, on the contrary, as we have reason to 
believe, a diminution of volume should accompany the change of state of the mate- 
rials of the earth from fluidity to solidity, the mean depth of the ocean would undergo 
gradual, though small alterations, over its entire extent at successive geological epochs, 
This result is easily deduced frum the general views contained in other writings of the 
author, whence it appears, that if the surface stratum of the internal fluid nucleus of 
the earth should contract when passing to the solid state, a tendency would exist to 
increase the ellipticity of the liquid covering of the outer surface of the crust. A 
very small change of ellipticity would suffice to lay bare or submerge extensive tracts 
of the globe. If, forexample, the mean ellipticity of the ocean increased from 51, to 
" a3 the level of the sea would be raised at the equator by about 228 feet, while under 
