78 
GEOLOGY OF THE FIRST DISTRICT. 
of the preceding for its own covering and protection. Most observers are aware that in the 
primitive districts of the United States where there is no limestone, the testacea are exceed¬ 
ingly rare; but wherever limestone or Jimestone and springs abounds, they are numerous. 
Testaceous animals are often seen on limestone rocks and pebbles, or on other shells both 
dead and alive, sucking off the carbonate of lime to serve their own purposes. The uniones 
are a good example of this fact; many of them are seen with a curved cavity, some with 
many on and near their beaks, which have been formed by taking a part of the superfluous 
covering from their fellows. 
Where there are limestone springs, some of the lime is continually carried into the brooks 
and marshes; so that it is constantly accumulating, and forming sinter and tufa, encrusting 
the vegetable and animal substances ; or deposited with the shells and other organic matters 
forming shell marl, for the future benefit of man. 
Those charae that secrete the greatest quantity of calcareous matter in their stems, are 
most abundant in the vicinity of limestone springs. 
It is a well known fact, that if the common hen be shut up where she can have no access 
to the earth, so as to scratch up the gravel and select such particles as contain lime, and if 
she be not fed with something containing lime, she either ceases to lay, or else the eggs have 
too slight a covering to protect the contents. 
Many birds eat chalk and sepia bone greedily during the breeding season. This is to sup¬ 
ply lime for the shells of their eggs, and for the bony matter of their animal system. Tame 
birds are often fed with sepia bone. The object is that just mentioned, and not for sharpen¬ 
ing their bills, as many suppose. 
It has been argued by Bakewell and others, that the polypi which form the coral reefs 
could not procure such quantities of lime from sea water, which contains very little, in con¬ 
sequence of their not having the power of locomotion; and that consequently it must -have 
been an organic product, combined by the vital powers from more simple elements. This 
conclusion is strengthened in his mind by the discovery of Sir Humphrey Davy, that the 
earths and fixed alkalies had metallic bases, and by the apparent metallization of ammonia 
when galvanized in contact with mercury. Now we know the ammonia to be composed of 
two gaseous bodies, nitrogen and hydrogen. He infers then by analogy that the other alka¬ 
lies and earths were constituted of more simple elements than we Avere acquainted with, and 
that the animals had the power of combining these from their food for their uses. 
The decomposition of ammonia to produce a metal, is a thing long since exploded. The 
whole superstructure built upon this foundation, of course, falls to the ground ; and the for¬ 
mation of lime from more simple elements than we are acquainted with, by organic combina¬ 
tion, as one of the columns of that structure, falls with it. 
Besides the failing of this argument, Mr. Bakewell does not seem to have considered, that 
although the zoophytes have not the power of locomotion, and although sea water contains 
but little lime, yet the currents are continually supplying the animals with a fresh supply of 
water, from which constant secretion of the lime may result, upon the same principle as we 
