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 

 60 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, hke 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 fossihfer- 

 ous beds are those consisting chiefly of the green 

 sand, and next, the thin calcareous stratums. 



* Report of Professor Henry D. Rogers to the Legislature of 

 New-Jersey. 



