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 hkely 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. 
Tt 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- 
