WHAT MAY BE LEARNED FROM EOZOON 141 



mentions as equally good those of the London clay at Brackle- 

 sham. But in no condition do modern Foraminifera, or those 

 of the Tertiary and Mesozoic rocks appear in greater perfection 

 than when filled with the hydrous silicate of iron and potash 



FIG. 14. Slice of Crystalline Lower Silurian Limestone ; showing 

 Crinoids, Bryozoa, and Corals in fragments. 



FIG. 15. Walls of Eozoon penetrated with Canals. The unshaded 

 portions filled with Calcite. (After Carpenter.) 



called glauconite or green earth, a substance now forming in 

 some parts of the ocean, and which gives, by the abundance of 

 its little bottle-green concretions the name of " greensand " to 

 formations of the Cretaceous age both in Europe and America. 



