1884.J NATURAL SCIENCES OF PHILADELPHIA. 25t 



a brownish color, and very rough and irregular, apparently the 

 effect of weathering. The grains can easily be crushed by the 

 finger-nail, thus exposing the internal green color. The granules 

 are coated with a laj'er of brown oxide of iron, within which shell 

 exists the unchanged nucleus of glauconite. 



The Indurated Marl, unless finely pulverized, has a lumpy ten- 

 dency, caused by numerous grains of green sand cemented by 

 the brown oxide of iron. In fact, the marl has, at certain points, 

 been almost entirely changed to brown oxide of iron, while in 

 other cases, seams of the latter penetrate the mass of the green 

 sand. Prof. Cook is of the opinion that the red sand of New 

 Jersey is due to the decomposition of green sand, whereby the 

 soluble salts have been carried away, leaving the insoluble siliceous 

 sand and red oxide of iron. We may, therefore, regard the belt, 

 which in New Jersey is called the red sand, and in Delaware the 

 indurated marl, as a true marl belt in a greater or less degree of 

 decomposition ; and while a slightly indurated green sand may 

 entirely differ mineralogically from a red siliceous sand, the dif- 

 ference is after all only one of degree of decomposition. 



Middle Marl Bed. 



This belt crosses the State with a uniform breadth of three and 

 a half miles, the northern line running from Port Penn, a little 

 north of Draw3'er's creek, and crossing the State line four miles 

 south of the Bohemia River. The southern line crosses the centre 

 of Noxontown mill-pond, keeping parallel with and a little south 

 of Appoquinimink creek. The middle marl bed (see II) is 

 divided into three very distinct layers: (1) A lowermost pure 

 green sand ; (2) an intermediate layer of friable shells, and (3) 

 an upper yellow or reddish 3ellow sand. The characters of these 

 several strata will be considered as follows : — 



Green Sand Layer. — This lowermost subdivision of the middle 

 marl bed occupies the main width of the belt to the north of 

 Appoquinimink Creek, and exhibits its principal exposures along 

 Drawyer's Creek and Silver Run, where its characters may be well 

 studied. It differs entirely from any of the foregoing varieties, 

 in that it is entire!}- free from calcareous matter, and shows none 

 of the general induration so characteristic of the previous forma- 

 tion. On the contrary, it is a very dry, pure green sand, which 

 varies in color from a deep bluish to a yellowish green, the latter 

 shade being due to a considerable admixture of siliceous sand. 



