254 GEOLOGY. 



South Carolina. It is very prominent in England, the 

 famous Dover Cliffs being composed of the chalk, and it 

 appears on the other side of the Channel, in France. It 

 also shows itself in other portions of France, and in vari- 

 ous parts of Europe. 



360. Source of the Chalk. Chalk is a marine deposit, 

 and it is supposed that it was made in water some two 

 or three hundred feet deep. It was made chiefly by 

 those minute animals called Foraminifera, the shells of 

 some of whose species are represented in Fig. 83, p. 157. 

 The evidence on this point is decisive. The observations 

 of Ehrenberg and others with the microscope show that 

 chalk is made up of shells, the foraminifera furnishing by 

 far the largest proportion of them. Ehrenberg states 

 that a cubic inch of chalk often contains over a million 

 of these microscopic organisms. Whenever you make 

 a mark with chalk upon the blackboard, you really de- 

 posit there a quantity of the shells of these organisms ; 

 and if your eyes could be suddenly endowed with a high 

 magnifying power, that white line would appear to you 

 like part of the wall of a grotto covered over with shells. 

 Indeed, the fact that the carbonate of lime has in any 

 case the form of chalk is owing to the aggregation of 

 these shells, they being so small that they give to the 

 rock formed from them a soft and porous character. 

 This character is not given to the rock under any ordi- 

 nary circumstances when it is formed from corals or 

 shells of any size. These same foraminifera are busy at 

 the present day taking from the water of the ocean car- 

 bonate of lime to form their shells, and these, being left 

 on the sea's bottom, have been found in some localities 

 to compose almost wholly the sand that has been brought 

 up in deep soundings. The material for chalk is then 

 being deposited, and the chalk which may thus be made 

 may at some future period be raised to the surface, and 

 constitute a part of the dry land of our earth. 



361. Flint in the Chalk. In England, and other coun- 



