1884.] natural sciences op philadelphia. 253 



Sand Marl. 

 The belt of sand marl runs from the river course to the south 

 of New Castle, gradually tapering in breadth as the Maryland 

 boundary line is reached. The southern limit of the belt, starting 

 at Delaware City, cuts the north corner of St. George's, and 

 keeps about a mile above the canal for the remaining distance 

 across the State. It may be described as a j^ellow sand, of a 

 greenish tinge, comprising a yellow siliceous sand mixed with 

 some green sand and a variable proportion of argillaceous matter. 

 No data are at hand for determining its thickness, except the 

 imperfect method of using width of outcrop and angle of dip, 

 according to which we find the sand marl stratum to have a 

 depth of 90 feet. 



Marl Beds. 



The marl beds cover a comparatively small area in the State, 

 and are practically limited to that division of New Castle county 

 called St. George's Hundred. 



The first important outcrops of green sand occur along the 

 Delaware and Chesapeake Canal, the channel of which cuts 

 deep into the formation. Its northern limit, as determined by 

 old marl pits, runs approximately parallel with the canal, keeping 

 a distance of from a quarter of a mile to a mile. From this line 

 the marl extends southward to another boundary parallel with, 

 and about one mile south of, Appoquinimink Creek, where it 

 gives place to the Tertiary clays. 



Subdivisions. — The divisions of the green sand formation are 

 found, with two exceptions, to correspond with those made by 

 the New Jersey Surve3^ In the first place, what is called by 

 Professor Cook the Upper Marl bed, is in Delaware, entirely 

 absent, and in the second place, the so-called Bed sand is either 

 entirely absent, or represented, as in the eastern part of the 

 State, by a much thinner stratum than is found in New Jersey. 

 This scanty development of the Bed sand is, however, compen- 

 sated for by a greater thickness of the Indurated green marl, 

 which, in Delaware, becomes the prominent parting laj'er between 

 the middle and lower marl beds. The chronological chart of 

 the Cretaceous (II), will show the divisions of the marl beds as 

 found in the State. 



Lower Marl Bed. 



This stratum, which extends as a narrow belt on each side of 

 the canal, is found to outcrop along the entire length of the 



