CONSTRUCTION OF THE EAKTH. 157 



that inhabit these 

 many -chambered 

 shells are com- 

 posed of a gelat- 

 inous fleshy sub- 

 stance, and have 

 minute prolonga- 

 tions which they 

 Fi s s3 - can throw out and 



retract, and which they use for swimming, crawling, and 

 gathering their food. There is great variety in the 

 shells of the different species, and the regularity, beauty, 

 and delicacy of structure of these shells are very won- 

 derful. In view of the vast amount of rocky material 

 which such minute animals have added in past ages, and 

 are now adding, to the earth's crust, it may well be said 

 that the additions made by the remains of the larger an- 

 imals, such as elephants, lions, crocodiles, whales, etc., 

 are utterly insignificant in the comparison. There is one 

 division of the foraminifera that are not microscopic, 

 viz., the nummulites, one of which you see at b. They 

 are of various sizes, from very minute up to the size of 

 an inch and a half in diameter." The name comes from 

 the Latin word nummus, money, because the shell re- 

 sembles a coin in shape. Sometimes limestone is com- 

 posed entirely, or nearly so, of nummulites, and then is 

 called nummulitic limestone. The Sphinx and the Pyr- 

 amids are made of this rock. It constitutes the princi- 

 pal part of several mountain ranges in the south of Eu- 

 rope, as the Alps and Pyrenees. 



In soundings in different parts of the Atlantic Ocean, 

 between Ireland and Newfoundland, as far south as the 

 Azores, there has been brought up a soft, sticky mud, 

 which has been called oaze. This, on being dried and 

 examined with the microscope, was found to consist of 

 the minute shells of foraminifera. As these shells are 

 composed of carbonate of lime, when an acid, as the sul- 



