GREEN SAND AND CRETACEOUS. 263 
form of small dark grains, about the size of grains 
of gunpowder. Their form is roundish, and they are 
very often composed of two or three smaller grains 
united together ; a distinctive feature by which they 
may at once be recognised from other dark kinds 
of sand. Though they contain on the average about 
50 per cent, of silica (the basis of flint), they are 
not gritty, but can be readily bruised between the 
teeth or upon the nail ; and some varieties, when 
moistened, admit of being kneaded into a half plas- 
tic mass, like impure clay. The prevailing colour 
of the grains is a deep green ; often a dull greenish 
blue, and not unfrequently a black chocolate colour. 
After having been exposed to the air for some time, 
this " marl" contracts a light gray hue, from the 
exterior grains becoming coated with a white in- 
florescence, which proves to be carbonate and sul- 
phate of lime. The following analysis, by Mr. Sey- 
bert, gives a fair average of the composition of the 
green grains : sihca, 49.83; alumina, 6; magnesia, 
1.83; potash, 10.12 ; protoxide of iron, 21.53 ; water, 
9.80 ; loss 0.89 == 100 grains. Some specimens con- 
tain as much as 5 per cent, of lime. The green sand 
forms a deposite over the whole southern part of 
New-Jersey of from 20 to 40 or more feet in thick- 
ness ; and as it is one of the most fertilizing agents, 
when applied to the soil, hitherto discovered, its 
value will be readily understood. A mine of gold 
would be of far less value to the state than its in- 
exhaustible beds of " marl." The diversified de- 
posites of sand, clay, green sand, limestone, and 
sandstone composing the cretaceous series in New- 
Jersey,* assume a great variety of aspects, resulting 
from their almost endless intermixture and their 
Various degrees of induration. The most fossilifer- 
ous beds are those consisting chiefly of the green 
sand, and next, the thin calcareous stratums. 
* Report of Professor Henry D. Rogers to the Legisltture of 
New-Jersey. 
