6 Beautiful Shells. 



get lime the same as that produced by burning the 

 white lumps from the chalk-pit, which lumps, by 

 the way, are said to be composed wholly, or for the 

 most part, of marine shells. This we should call 

 cretaceous matter, from creta, which is the Latin for 

 chalk, or calcerous, from calcis — lime. Granular 

 shells you have been told are sometimes called 

 concretionary, this is because they contain a large 

 amount of this chalky deposit. The rock called 

 limestone, geologists tell us, is composed entirely 

 of fossil shells and mud, or what was once mud, 

 dried and hardened, most likely by extreme heat, 

 to the consistence of rock. Wonderful this to 

 think of; huge mountains, and mighty masses, and 

 far-stretching strata, forming a large portion of the 

 crust of the earth, made up chiefly of the coverings 

 of fishes, a great portion of them so small as to be 

 scarcely visible to the naked eye. — Truly wonderful! 

 But we shall have more to say upon this head when 

 we come to speak of Fossil Shells, as well as on 

 the subject of Pearls, in our chapter on the fish in 

 whose shells they are chiefly found. 



It has been a matter of dispute with natu- 

 ralists whether the testaceous mollusks have shells 

 at all before they issue from the egg, and the main 

 evidence favours the opinion that, generally speak- 



