695 
conspicuous in the adult ;’ Mr. Owen remarks, that notwithstanding 
the prominent end of the symphysial part containing the chief por- 
tion of the tusk-socket is wanting, yet ‘‘ two foramina are recognized 
at the anterior part of the chin,” and these, he observes, must be 
either portions of the alveoli of the tusks, or the canals of the nerves 
and vessels for the tusks in these alveoli. 
Thus, Mr. Owen says in conclusion, all the examples which:seemed 
to show that the genus Mastodon at no period of life possessed tusks 
in the lower jaw, and that the genus Tetracaulodon was characterized 
at all periods of life by two projecting tusks in the lower jaw, become 
invalidated on a close inspection, and enter into the series of facts 
which support the proposition that the Mastodon giganteum has two 
lower tusks originally in both sexes, and retains the right lower tusk 
only in the adult male. 
March 9.—The followmg communications were read : 
1. A paper on the Salt Steppe south of Orenburg, and on a re- 
markable freezing Cavern. By Roderick Impey Murchison, Esq., 
Pres. G.S. ' 
(1.) This salt steppe is distinguished from many of those which 
are interposed between the Ouralsk and the Volga or are situated 
on the Siberian side of the Ural Mountains, by consisting not of 
an uniform flat resembling the bed of a dried-up sea, but of wide 
undulations and distantly separated low ridges; nevertheless it is, 
Mr. Murchison states, a true steppe, being devoid of trees and little 
irrigated by streams. The surface consists of gypseous marls and 
sands, considered by the author to be of the age of the zechstein*, 
and it is pierced in the neighbourhood of the imperial establishment 
of Illetzkaya Zatchita by small pyramids of rock-salt. These pro- 
truding masses attracted the attention of the Kirghiss long before 
the country was colonized by the Russians, but it is only during a 
short period that the great subjacent bed has been extensively 
worked. The principal quarries, exposed to open day, are situated 
immediately south of the establishment, and have a length of 300 
paces, with a breadth of 200 and a depth of 40 feet. The mass of 
salt thus exposed, is of great purity, the only extraneous ingredient 
being gypsum, distantly distributed in minute filaments. At first — 
‘sight the salt seems to be horizontally stratified, but this apparent 
structure, Mr. Murchison states, is owing to the mineral being ex- 
tracted in large parallelopipedal blocks twelve feet long, three feet 
deep and three wide. On the side where the quarry was first 
worked, the cuttings presented, in consequence of the action of the 
weather, a vertical face as smooth as glass, but at its base there 
was a black cavern formed by the water which accumulates at cer- 
tain periods of the year, and from its roof were saline stalactites. 
-* His extensive surveys of Russia have convinced Mr. Murchison that 
rock-salt and salt springs occur in all the lower sedimentary rocks of that 
empire, from great depths below the Devonian or old red sandstone system 
to the zechstein and the overlying marls and sandstones. 
