118 
ARTESIAN WELLS ON THE ATLANTIC COAST. 
[bull. 138. 
CHARACTERISTICS OF THE FORMATIONS. 
RARITAN AND POTOMAC. 
The basal members of the Coastal Plain series in Delaware comprise 
the upper portion of the Potomac formation below and more or less of 
the southward extension of the Earitan beds above, but they appear 
not to be clearly separable. The deposits consist of clays and sands 
interbedded and intermingled in various relations. According to 
Chester, red clays predominate above and fire clays and sands below. 
The basal beds appear to consist largely of coarse sands, which lie on 
the steeply east-dipping floor of crystalline rocks and contain water 
available for wells. It is probable that this basal series was penetrated 
in the well at Middletown, in which rock was reported at a depth of 
552 feet. The Earitan beds are overlain by white and buff sands with 
more or less clay and marl intermixture to the eastward, which are 
probably the representatives of the Magothy formation of Maryland, 
but a careful study of this question has not yet been made. 
CRETACEOUS MARL SERIES. 
The middle and lower marl beds of NeAv Jersey and their associated 
beds extend across Delaware in a belt averaging about 8 miles wide, of 
which the greater part lies between Middletown and Delaware City. 
They are extensively exhibited along the Delaware and Chesapeake 
Canal. In the vicinity of this canal they dip south 30° east at a rate 
of 45 feet per mile, according to Chester, but the rate decreases south- 
ward. The following beds are recognized by Chester: 
Formation. 
Division. 
Material. 
Thick- 
Feet. 
Middle marl 
Redbank . 
Lower marl. 
Yellow sand 
Shell layer 
Greensand layer 
Indurated greensand 
Red sand 
Black marl 
Shell layer 
Cretoidal marl 
Contains some greensand 
Shells of Rancocas age 
Dry, pure greensand ; no clay 
Lumpy, dark-colored rich marl, with some clay. 
Soft, yellowish-red sand 
Mainly a black, micaceous acid clay 
Shells in black, earthy marl 
Tough, bluish-black marl, with some clay 
3-10 
«32 
3 
a 25 
About. 
These subdivisions present notable differences from the New Jersey 
marl series, particularly in the case of the Redbank, which changes 
from a coarse water-bearing sand to a marl bed above and a fine yel- 
lowish sand below. This change continues southward into Maryland, 
where the subdivisions are not so strikingly marked and the formations 
have been consolidated into one, known as the Severn formation. 
