LAURENTIAN LIFE 



lis 



representing all the forms of the interior, and any 

 pores that may have penetrated the walls, and also 

 perfectly representing the soft gelatinous body of 

 the animal which once tenanted the shells (Fig. 24). 

 (See also Fig. 25 at end of chapter.) 



Fig. 24. — Cast 0/ Cavities of Folystomella in daiuoHUe {)nagnified). 

 After a photograph from Dr. Carpenter, and mounted specimens from his collection. 



When we examine oceanic sediments of older 

 date, we find similar fillings in limestones, chalks, 

 and sandstones of various ages, some of the latter 

 containing glauconite so abundantly as to bear the 

 name of greensands, from their colour ; and in 

 these older examples we more frequently find alu- 



