38 THE POPULAR SCIENCE MONTHLY. 



Cont-emporaneously with these observations, the indofatigable 

 Ehrenbcrg had discovered that the " greensands " of the geologist 

 were largely made up of casts of a similar character, and proved the 

 existence of Foraminifera at a very ancient geological epoch, by dis- 

 covering siich casts in a greensand of Lower Silurian age, which oc- 

 curs near St. Petersburg. 



Subsequently Messrs. Parker and Jones discovered similar casts 

 in process of formation, the original shell not having disappeared, 

 in specimens of the sea-bottom of the Australian seas, brought 

 home by the late Prof. Jukes. And the Challenger has observed a 

 deposit of a similar character in the course of the Agulhas current, 

 near the Cape of Good Hope, and in some other localities not yet 

 defined. 



It would appear that this infiltration of Foraminifera shells with 

 Glauconite does not take place at great dejiths, but rather in what 

 may be termed a sublittoral i-egion, ranging from 100 to 300 fatlioms. 

 It cannot be ascribed to any local cause, for it takes place, not 

 only over large areas in the Gulf of Mexico and the coast of 

 Florida, but in the South Atlantic and in the Pacific. But what 

 are the conditions which determine its occurrence, and whence 

 the silex, the iron, and the alumina (with perhaps potash and some 

 other ingredients in small quantity) of which the Glauconite is com- 

 posed, proceed, are points on which no light has yet been thrown. 

 For the present we must be content with tlie fact that, in certain 

 areas of the " intermediate zone," greensand is replacing and repre- 

 senting the primitive calcareo-silicious ooze. 



The investigation of the deposits which are now being formed in 

 the basin of the Mediterranean by the late Prof. Edward Forbes, 

 by Prof. Williamson, and more recently by Dr. Carpenter, and a 

 comparison of the results thus obtained with what is known of the 

 surface fauna, have brought to light the remarkable fact that, while 

 the surface and the shallows abound with Foraminifera and other 

 calcareous-shelled organisms, the indications of life become scanty at 

 depths beyond 500 or 600 fathoms, while almost all traces of it disap- 

 pear at greater dej^ths, and at 1,000 to 2,000 fathoms the bottom is 

 covered with a fine clay. 



Dr. Carpenter has discussed the significance of this remarkable 

 fact, and he is disposed to attribute the absence of life at great 

 depths partly to the absence of any circulation of the water of the 

 Mediterranean at such depths, and partly to the exhaustion of the 

 oxygen of the water by the organic matter contained in the fine 

 clay, which he conceives to be formed by the finest particles of the 

 mud brought down by the rivers which flow into the Mediterranean. 



However this may be, the explanation thus offered of the presence 

 of the fine mud, and of the absence of organisms which ordinarily 

 live at. the bottom, docs not account for the absence of the skeletons 



