Vol. 58. ] ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixvil 
an important influence on the nature of the deposits. The work of 
Russian observers in the Black Sea, and that of Murray & Irvine, 
to which reference has already been made, is so suggestive and 
important from the latter point of view, that I make no apology for 
giving a brief account of it, especially as it introduces a new idea. 
The surface-waters of the Black Sea contain free oxygen, and 
support an abundance of organic life; but the deeper and denser 
waters are charged with sulphuretted hydrogen, and the only 
organisms present are anaérobic bacteria. The amount of sul- 
phuretted hydrogen increases with depth. At100 fathoms there are 
33 cubic centimetres in 100 litres, at 200 fathoms 222 ¢.c., and at 
1185 fathoms 655 c.c. According to the researches of Zelinsky and 
Brussilovsky, the anaérobic bacteria play an important part in the 
chemical changes which result in the formation of sulphuretted 
hydrogen. Several bacteria have been observed, but one only (Bac- 
terium hydrosulphuricum ponticum ) has been studied in detail. This 
bacterium possesses the power of liberating sulphuretted hydrogen, 
not only from organic matter containing sulphur, but also directly 
from sulphates and sulphites ; and the authors just named maintain 
that the whole of the sulphuretted hydrogen in the sea-water has 
been derived from the sulphates in this way. While accepting the 
view that a large part of the sulphuretted hydrogen has thus been 
formed, Prof. Andrussov believes that a portion of it is due to the 
putrefaction of the sulphur-bearing organic matter which falls from 
the surface into the deeper stagnant waters. But all are agreed 
that the sulphates of the sea-water are acted upon, and that as a 
final result sulphuretted hydrogen and carbonates are formed. 
Changes of the opposite kind take place in the zone where the 
water containing sulphuretted hydrogen comes into contact with 
that containing oxygen. This zone occurs at a depth of about 
200 fathoms. Here the sulphuretted hydrogen becomes oxidized, 
and sulphates are formed at the expense of carbonates. According 
to the researches of Yegunov and Vinogradski, the change is 
brought about by the so-called sulphur-bacteria. Like the iron- 
bacteria, which give rise to important deposits of bog-iron ore, and 
the nitrifying bacteria which produce saltpetre and probably assist 
in the decomposition of many rocks, these sulphur-bacteria derive 
the energy necessary for their existence from the oxidation of 
inorganic compounds. Sulphuretted hydrogen and carbonates are 
necessary for their existence. They separate sulphur in their cells 
in the form of soft oily globules, and the oxidation of this sulphur 
