GEOLOGICAL SOCIETY OF DUBLIN. 
77 
3rd Law.—The compression in a cleaved rock is greatest in a direc¬ 
tion perpendicular to the planes of cleavage. 
These positions are illustrated in the Eev. Professor’s papers by some 
very interesting drawings of distorted fossils from the Carboniferous 
Limestone. 
Professor H. D. Eogers, however, does not entirely subscribe to these 
views, for in a learned paper by him, published in the Transactions of 
the Eoyal Society of Edinburgh, “ On the Laws of Structure of the more 
disturbed zones of the earth’s crust,” he adheres rather to the theory of 
Professor Sedgwick, and conceives that “ cleavage is a change brought 
about by the parallel transmission of planes or waves of heat, awaken¬ 
ing the molecular forces and determining their direction.” 
Mr. Hopkins has also contributed some experimental researches on 
the conductive powers of various rocks, and the bearing of the results 
upon theories of terrestrial temperature. It is by the accumulation of 
such facts as these that we shall ultimately be led to the construction of 
a true and philosophical theory of the earth. 
It is satisfactory to find one of our Professors, Mr. Hennessy, grap¬ 
pling with one of these arduous questions of mixed mathematics, and at¬ 
tempting to calculate the forces capable of changing the sea-level during 
different geological periods. Arguing on the supposition that the crust 
of the earth underwent a change of volume on the gradual cooling of its 
surface, and that a change of the ellipticity would be the consequence, 
he concludes that a very considerable alteration of the sea-level would be 
the inevitable result. 
Mr. Oldham gave us a general view of the geology of India. It is 
a gigantic subject, and the great scale on which the principal formations 
in that country are to be seen must ultimately be most important to the 
progress of our science. We are under the greatest obligations to the 
late Mr. Greenough, one of whose last works was the publication of his 
Map of India; like the similar Map of Great Britain, it will form the 
groundwork for all future inquirers. But in so vast a country, and one 
which contains so many large tracts, as yet but little known to the na¬ 
tives themselves, it will require many years of careful exploration before 
the true nature and extent of the different strata can be accurately de¬ 
termined. Mr. Oldham’s work has, doubtless, been arrested by the 
deplorable events which have recently occurred in that country, but we 
must hope that general tranquillity will soon be restored, and that the 
Sepoy will soon rank with the Sivatheria and other extinct animals. 
We are also indebted to the Cavaliere Meneghini for an interesting 
paper on the Palaeontology of Tuscany. Itself the birthplace of this 
branch of our science, it appears that there are not wanting patient 
inquirers to assist Professor Sair in following up and correcting the con¬ 
clusions of the distinguished Brocchi. 
Mr. E. Goodwin Austen, whose researches on the chalk and underly¬ 
ing formations have created such interest, favoured us with a communi¬ 
cation on the occurrence of a granite boulder in the chalk. 
vol. v.— proc. soc. 
M 
