THE ORIGIN OF LIFE 261 



others, their size and importance have diminished, 

 and the grander forms of more recent times have 

 some of them been fain to build up their hard 

 parts of cemented sand instead of Hmestone. 



But we further find that, while the first though not 

 the only organic gatherers of limestone from the 

 ocean waters, they have had to do, njt merely with 

 the formation of calcareous sediments, but also with 

 that of silicious deposits. The greenish silicate 

 called glauconite, or greensand, is found to be 

 associated with much of the foraminiferal slime now 

 accumulating in the ocean, and also with the older 

 deposits of this kind now consolidated in chalks and 

 similar rocks. This name glauconite is, as Dr. Hunt 

 has shown, employed to designate not only the 

 hydrous silicate of iron and potash, which perhaps 

 has the best right to it, but also compounds which 

 contain in addition large percentages of alumina, or 

 magnesia, or both ; and one glauconite from the 

 Tertiary limestones near Paris is said to be a true 

 serpentine, or hydrous silicate of magnesia.^ Now 

 the association of such substances with Foraminifera 

 is not purely accidental. Just as a fragment of 



* Berthier, quoted by Hunt. 



