GEOLOGICAL SOCIETY OF DUBLIN. 
171 
Steropis ( Limulus) anthrax {Prestwick). “ Geological Transactions,” 
second series, 5, t. 41, Fig. 1-4. 
„ ,, rotundus. Ibid., Fig. 5-7. 
,, „ trilobitoides. Ibid., Fig. 8; and Buckland’s 
“ Bridgewater Treatise,” p. 396, t. 46, Fig. 3. 
,, ,, trilobitoides {f.T). Portlock’s 1 ‘Report,” t.24,Fig.ll. 
Synonyms of this Species. 
Steropis {Entomolithus monoculus). Martin, “ Pet. Derb.,” t. 45, 
Fig. 4. 
,, {Bellinurus bellulus). Konig, Icon. Sect., PI. 18, No. 230. 
The President stated that this was the first specimen of a Limulus 
found in those coal-measures. 
Mr. Baily stated, in answer to the President, that only three heads 
had been found, and not the tail. 
Professor Kinahan considered the absence of spines a strong confir¬ 
mation of Mr. Baily’s view as to separating these specimens into a new 
genus. 
Mr. Kelly made some remarks. 
The President then read the following letter— 
ON THE ORIGIN OF MAGNESIAN LIMESTONE. BY CAPTAIN CHARLES P. MOLONY, 
OF THE MADRAS ARMY. 
Various opinions have, from time to time, been put forward regarding 
the way in which magnesian limestone has been formed. Some say that 
it is a stratified magnesian limestone. Others deny this, and argue that 
it must have been formed by infiltration. Others, again, maintain that 
it was originally a stratified rock formed by the deposition of carbonate 
of lime, but that it was afterwards altered or changed into a magnesian 
limestone by the impregnation of magnesian vapours given off by neigh¬ 
bouring igneous rocks when in a heated state. Another party assert 
that it was at first deposited in regular strata of carbonate of lime, or 
the common gray limestone, but that, at a subsequent period, water, 
holding carbonate of magnesia in solution, passed over the rocks, which, 
having great absorbent powers, like lump sugar, drank in, in course of 
time, sufficient carbonate of magnesia from the water to change them 
into magnesian limestone. 
Dr. Apjohn has clearly shown that the rock could not have inhaled 
magnesia from vapours given off by igneous rocks when in a molten or 
heated state, as magnesia is not capable of being vaporized. 
The almost total absence of fossils in these rocks is also brought 
forward, “ and with truth,” as proof that they could not have been ori¬ 
ginally stratified rocks that were afterwards altered into magnesian lime¬ 
stone either by absorption or by impregnation; for, if they were, the 
animals that were embedded in the limestone strata at the time of their 
deposition would still remain in the rocks. 
