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PROCEEDINGS OE SOCIETIES. 
bably non-fossiliferous, Old Red Sandstone. Both these subdivisions— 
namely, the carboniferous slate and yellow sandstone—are so immediately 
connected, and pass so insensibly into each other, stratigraphically as 
well as by fossils, that I have classified them on the map as one series, 
under the term “ yellow sandstone group.” 
It is in the carboniferous slate or shale, the upper member of this 
group, at Lispatrick and other localities of the same district, near the 
Old Head of Kinsale, in the county of Cork, that the impressions of 
Posidoniae occur, to which I have referred; and they are accompanied 
by numerous other ordinary carboniferous fossils, especially by the Go- 
niatites striolatus, the surface of which is ornamentally pyritised; and 
I may in addition enumerate Orthis crenistria , Spirifer attenuatus, Tur- 
linolia fungites, &c. There is much difficulty in this locality in pro¬ 
curing specimens in a sufficiently perfect state for identification, the 
portions of the impression most necessary for that purpose being gene¬ 
rally imperfect, owing to the scaling and crumbling nature of the shale, 
as well as to the distortion produced by the action of cleavage on the one 
hand, and, on the other, by those portions remaining hidden in the rock 
being cut off by innumerable cross or dip joints, which are frequently 
less than half an inch asunder; and in this respect they are quite similar 
to those which occur in the Calp of Rush. The Posidonia lateralis * now 
before us, as represented in the diagrams I have prepared, will be seen 
to have been much extended in the direction of the longer axis of the 
shell by the action of cleavage, but I think the distortion will yet hardly 
amount to such a degree as to render the specimens incapable of identi¬ 
fication with those usually figured as P. lateralis. The impression,-j- as 
represented in the diagram beneath the former, may possibly be the same 
species, the extension being parallel to the direction of the shorter dia¬ 
meter of the shell; but I shall leave the consideration of this subj ect in the 
hands of the Reverend President, who is so much better qualified than I 
am to discuss its bearings, not only from the attention which he has 
already directed to it, but from the researches in which he is at the 
present moment engaged, and from which we may expect in future such 
valuable results. J 
Immediately accompanying the Posidonia lateralis , in the same bed, 
I have discovered a very beautiful and remarkable Avicula, || which is 
represented by the lower figure in one of the diagrams; and as I do not 
remember to have seen it before, it may probably be new, but it is at 
least very valuable from the unusually perfect state in which it is pre¬ 
served,—a circumstance which is very rare in cleavable rocks, as may 
* See Plates XVI., XVII. f See Plate XIX., Fig. 2. 
X Note added in the Press .—Subsequently to the printing of my paper, the President 
has kindly undertaken to add a note in reference to the effect which cleavage produces 
in the distortion of fossil forms. The note alluded to is printed in full, page 161. Mr. 
Haughton has also given a review of the genus, which, it is to be hoped, will tend to sim¬ 
plify its specific diagnosis.—R. G. 
|| This fossil has been unfortunately mislaid in London, so that, being unable to figure 
it sufficiently accurately, I prefer to omit it in the Plates.—R. G. 
