Ill EXPEDITION OF THE " CHALLENGER " 93 



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 Fora- 

 minifera shells with G-lauconite does not take place 

 at great depths, but rather in what may be 

 termed a sublittoral region, ranging from a 

 hundred to three hundred fathoms. 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 composed, 

 proceed, is a point on which no light has yet been 

 thrown. For the present we must be content 

 with the fact that, in certain areas of the 

 " intermediate zone," greensand is replacing and 

 representing the primitively calcareo-silicious 

 ooze. 



The investigation of the deposits which are 

 now being formed in the basin of the Mediterra- 

 nean, by the late Professor Edward Forbes, by 

 Professor 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 



