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. It cannot have 

 been long ago, geologically speaking, because the shells of Drcissensia 

 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- Cow 



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. S. 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. E. Lepsius, of Darmstadt. 



Halithermm schinzi 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 



