GEOLOGICAL SOCIETY OF LONDON. 



Urals. Of its southern limits no precise lines were given, 

 but it was said to occur at intervals on the eastern flanks of 

 the Southern Urals, in the steppes of the Kirghise. It is 

 found at all levels, to the height of 400 feet, and varies in 

 thickness from two to twenty feet. It consists of fine black 

 particles, mixed with grains of sand ; and when wet forms a 

 terraceous mass, but becomes an impalpable powder when 

 dry. The following is the analysis : — silica 69*8 ; alumina 

 13*5 ; lime 1*6 ; oxide of iron 7 ; vegetable matter 6'4 ; traces 

 of prussic acid, sulphuric acid, chlorine, and loss, 1*7. Mr. 

 Murchison states that he thinks this deposit is of the same 

 age as the Loess of the Rhine, though it contains no fluvia- 

 tile or terrestrial testacea, and because it occurs in plateaux ; 

 this is not the case with the latter. He also believes it to be 

 a submarine accumulation, deposited under quiet circum- 

 stances. 



April 6th and 20th, 1842.— R. J. Murchison, Esq., Presi- 

 dent, in the chair. 



A notice was first read " On the Tetracaulodon/' by Mr. 

 Koch. 



The object of this communication is to support the opinion 

 that the tetracaulodon is generically distinct from the mas- 

 todon, and consequently that the tusks in the lower jaw are 

 not merely sexual characteristics. Mr. Koch states, that 

 during his residence in the United States, he examined nearly 

 all the inferior jaws of the mastodon which had been pre- 

 served in public and private collections, but in no one in- 

 stance did he ever observe any traces of a tusk; and Dr. 

 Hays, of Philadelphiaj is reported to have arrived at a similar 

 conclusion respecting at least forty specimens of lower jaws. 

 Mr. Koch refers particularly to the mastodon in the Phila- 

 delphia Museum, and that preserved at Baltimore, both of 

 which, he says, must have belonged to males. He then 



