118 WORMS, MOSS-POLYPS, SPONGES, ETC. 



line, or, what is more usually the case, in one or 

 more circles around the initial sphere. A com- 

 plex arrangement of chambers may thus be built 

 up, especially if the system of development has 

 proceeded along more than a single plane. Of 

 such a complex character is our little Rotalia of 

 the ocean sands, the different chambers in the shell 

 of which can be clearly traced out with the aid of 

 the microscope. 



The Foraminifera lead an apparently very, inde- 

 pendent life on the ocean wave, tossed hither and 

 thither among the seething waters : their home is 

 not merely the surface, but extends to the gloomier 

 shades of the abyss. At the bottom of the sea the 

 shells of the dead animals accumulate in prodigious 

 numbers, forming there a deep white or gray mud 

 known as the ' Atlantic ooze.' It is this same sub- 

 stance compacted which constitutes true chalk, and 

 likewise much of the hard limestone and marble 

 which we see everywhere about us. At one time 

 the areas where we now find chalk and marble 

 were beneath the sea, but through movements of 

 the earth's crust of one kind or another they have 

 been brought to their present inland positions. 

 The so-called ' greensands' or ' marls' of New Jer- 

 sey are largely a foraminiferal composition, the 

 little green pellets of the mineral glauconite, 

 which give the distinctive appearance to the sand, 

 representing principally the fillings or casts of an 

 endless number of foraminiferal shells, from which 

 the lime has been removed through solution. 



