298 NATURAL SCIENCE [November 
The action of these deep-sea bacteria is truly remarkable. In 
other seas the rain of dead organisms from the surface plankton 
forms the food of other organisms living in the depths. But here 
the rain, after it has fallen through the upper 100 fathoms, finds 
no organisms to eat it. The microbes have it all to themselves. 
The albumen of the descending dead organisms putrefies under the 
influence of the bacteria; oxygen is taken from it to form carbon 
dioxide, and hydrogen sulphide is evolved. The carbon dioxide 
appears to help in the formation of the fine precipitate of carbonate 
of lime that is found in the depths. The hydrogen sulphide partly 
acts on the salts of iron in the water, forming iron sulphide, partly 
decomposes as it reaches the oxygen of the surface. 
The gradual establishment of this peculiar state of things can 
be traced. Geological evidence shows that in Oligocene and 
Miocene times the Euxine and Caspian basins were connected, only 
being separated by the final upheavals of the Caucasus. Connection 
with the Aegean was due probably to the cutting down and lower- 
ing of a river-channel, of which the Bosphorus and Dardanelles are 
the remains. When this took place is uncertain. IJt cannot have 
been long ago, geologically speaking, because the shells of Drezssensia 
and other brackish-water molluscs are found lying on the bottom of 
the Black Sea at depths where neither they nor any animals can 
now exist. On the other hand the northern character of the Black 
Sea fauna, notably the presence of the common porpoise, suggests 
that the connection existed already during the Glacial Period. 
Further interesting details, together with a description of the 
deposits now forming in the Black Sea, will be found in Professor 
Andrussov’s guide. We have merely quoted enough to show the 
intimate relations between geology and oceanography, relations which 
we are glad to see officially recognised by the International Congress. 
AN EXTINCT SEA-CoWw 
Last month (p. 223) we briefly referred to our unfortunate lack of 
knowledge of the ancestors of the Sirenian mammals commonly 
known as sea-cows. In reference to this subject, we have now 
been favoured by Mr A. 8. Woodward, of the British Museum, with 
the accompanying restored drawing of the skeleton of the best- 
known extinct Tertiary Sirenian, Halitherium, which he has recently 
had prepared for a forthcoming work on Vertebrate Palaeontology. 
This figure (p. 299), which is of about one-fifteenth the natural size, 
is mainly based upon a skeleton in the Museum of Mayence and 
upon the researches of Dr G. R. Lepsius, of Darmstadt. 
Halitherium schinet is found in the Lower Miocene sands of 
Hesse Darmstadt, and so dates back to the early part of the Ter- 
tiary period, It will be seen, nevertheless, that it only differs from 
