92 EXPEDITION OF THE &quot; CHALLENGER &quot; 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 &quot; a mixture, in about 

 equal proportions, of Gldbigerincc and black sand, 

 probably greensand, as it makes a green mark 

 when crushed on paper.&quot; Professor Bailey, 

 examining these grains microscopically, found 

 that they were casts of the interior cavities of 

 Foraminifcra, consisting of a mineral known as 

 Glauconitc, 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 &quot; greensands &quot; of the geologist were largely 

 made up of casts of a similar character, and proved 

 the existence of Foraminifcm 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 



