62 Geological Society. 
tusk in the presumed male Mastodon’s jaws of corresponding size, 
and considered by Dr. Hays to constitute a distinct variety, if not a 
new species of Tetracaulodon, Mr. Owen considers it to be the jaw of 
a young female Mastodon in which the obliteration of the tusks had 
not been completed. 
A lower jaw without tusks, considered by Dr. Hays to have been 
a young Mastodon, but with “the chin slightly broken, so that it is 
impossible to determine whether it had the foliated termination so 
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 following 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. [An abstract of this paper has been inserted in vol. xxi. 
p- 357.] 
2. Extracts from a letter addressed by Sir J. Herschel, Bart., 
F.G.S., to Mr. Murchison, explanatory of the Phenomena of the 
Freezing Cave of Illetzkaya Zatchita. [See p. 359 of vol. xxi.] 
3. “On some Phzenomena observed on Glaciers, and on the in- 
ternal temperature of large Masses of Ice or Snow, with some Re- 
marks on the natural Ice-caves which occur below the limit of per- 
petual Snow.” By Sir John Herschel, Bart., F.G.S., &e. [See 
p- 362 of vol. xxi. | 
A paper “On Rock-Basins in the Bed of the Toombuddra, South- 
ern India (lat. 15° to 16° N.),” by Lieut. Newbold of the Madras 
Army, was then read. 
Rock-basins abound in the beds of many rivers in southern India, 
particularly where rapids and falls are of frequent occurrence; but 
in none are they more numerous and better exhibited in their va- 
rious stages of formation than in the Toombuddra. In the bed of 
this river, near the island of Desanur and below the falls caused by 
the anicut or ancient stone embankment thrown across the channel 
for purposes of irrigation, is a great number of these cavities ge- 
nerally of a circular and oval form, and of various dimensions, 
equal, in one instance, to 12 feet in circumference and 4 feet 
in depth. Upwards of 130 basins were observed here and near 
the ruins of Bijanugger (lat. 15° 14, long. 76° 37’), On many 
large bare slabs of rock are chains of these cavities connected by 
