92 EXPEDITION OF THE " CHALLENGER " m 



scientific hydrography, observed, that the mud 

 forming the sea-bottom at depths of one hundred 

 and fifty fathoms, in 31 32' N., 79 35' W., off 

 the Coast of Florida, was " a mixture, in about 

 equal proportions, of Globigerince and black sand, 

 probably greensand, as it makes a green mark 

 when crushed on paper." Professor Bailey, 

 examining these grains microscopically, found 

 that they were casts of the interior cavities of, 

 Foraminifera, consisting of a mineral known as 

 Glauconite, which is a silicate of iron and alumina. 

 In these casts the minutest cavities and finest 

 tubes in the Foraminifer were sometimes repro- 

 duced in solid counterparts of the glassy mineral, 

 while the calcareous original had been entirely 

 dissolved away. 



Contemporaneously with these observations, 

 the indefatigable Ehrenberg had discovered that 

 the " green sands " 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 discovering such casts in a 

 greensand of Lower Silurian age, which occurs 

 near St. Petersburg. 



Subsequently, Messrs Parker and Jones dis- 

 covered 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 Professor Jukes. And the 

 Challenger has observed a deposit of a similar 



