344 MARL. — GRANITE. 
to it when withdrawn. There is a kind of clay 
produced by the decomposition of feldspar, which 
closely resembles marl ; it is, however, easily dis- 
tinguished by its not etfervescing when mixed with 
vinegar, oil of vitriol, or any other acid, as marl 
does. This substance contains from 40 to 95 per 
cent, of carbonate of lime, with a quantity of vege- 
table matter, sand, phosphate of lime, and a trace of 
magnesia. Its immense value as a fertilizing agent 
will be noticed in the ensuing chapter. 
We have already described, at sufficient length, 
perhaps, the localities of the green sand marl^ which 
forms a deposite over nearly the whole southern 
half of New-Jersey. It has been traced in many 
places through the Atlantic States to Alabama, and 
has lately been discovered by Professor Hitchcock 
in Massachusetts, and by Dr. Troost in Tennessee. 
The green marl of Massachusetts consists chiefly of 
silex, alumine, and oxide of iron, and does not con- 
tain potash like that of New-Jersey : hence there 
is much doubt as to its possessing such powerful 
fertihzing properties as that of the latter. This can 
only be tested by actual experiment. The marls of 
Virginia and the Middle States, however, are chiefly 
of the miocene era, and composed of carbonate of 
lime (mostly derived from shells), from 12 to 90 per 
cent. 
Granite. — We have given so full a description of 
the granite formation in the United States, that lit- 
tle need be added in this place. For building pur- 
poses, no country in the world possesses such an 
inexhaustible quantity and variety of granite rocks 
as New-England ; none more durable in structure, 
or beautiful in appearance. 
Of the Eastern States, Maine is pre-eminent for 
the abundance and excellent quality of her various 
granite rocks, which offer facihties for quarrying 
and exportation unequalled by those of any other 
part of the known world. Here all varieties are to 
