20 
ARTESIAN WELLS ON THE ATLANTIC COAST. 
[BULL. 138. 
at D would not. In case this fining of materials was mainly in irregu- 
lar beds or in local areas, the districts underlain by water would be 
restricted to the areas of coarse materials. 
This relation is probable throughout the Coastal Plain, for the old 
shore of the deposits was near A, and the fineness of materials increases 
offshore in most if not all of the formations. Beds which contain much 
water to the westward sometimes prove to be entirely fine-grained and 
barren of water to the east and southeast. 
A third condition, which is quite widespread in Virginia from 
Fredericksburg southward, is shown in section 3. This represents an 
^''V/VTrp^Jv 
•/'"^ 
'o> rock ^y^s^\^:^77^7Vyr?^^^^;^^^^^m 
Fig. 2. — Ideal sections illustrating certain general conditions affecting underground waters. 
overlap of fine materials across the catchment outcrop of the coarse 
beds, and this relation probably greatly diminishes the amount of water 
in the permeable bed. In Virginia the Pamunkey and Potomac for- 
mations are overlapped in this way by the clays of the Chesapeake 
and the loams of the Lafayette and the Columbia, and although they 
are more or less widely bared of these deposits in the river depres 
sions, their water supplies are cut off for considerable widths on the 
divides. 
Section 2 is introduced to illustrate the reason why some of the beds 
to the westward which hold water have not yielded or possibly may not 
yield water to the eastward. 
Section 3 has a somewhat similar practical bearing, but beds which 
are widely overlapped by impermeable deposits in one part of the 
