180 ARTESIAN WELLS ON THE ATLANTIC COAST. [bull. 138. 
WATER HORIZONS IN EASTERN VIRGINIA. 
The greater part, if not all, of the Coastal Plain region of Virginia 
is underlain by water-bearing strata, of which to the eastward there 
are several horizons. The failures to obtain the higher water in some 
of the wells near the bay indicate that in this area at least there are 
no good water supplies in the higher horizons, but the waters of the 
lower horizons have not yet been fully developed. The success of the 
new well at Fort Monroe definitely proves the existence of one of these. 
The failure of a single well, as at North End Point, does not always dis- 
prove the existence of a water horizon, for we know of many instances 
in which water has been passed unnoticed, or willfully, by well borers. 
The principal water horizons in eastern Virginia are the Chesapeake, 
the Pamunkey, and the Potomac. 
POTOMAC. 
There is more or less water in all of the coarser sand beds of the 
Potomac formation, but the principal supplies may be expected from 
the sands and gravels of the basal members lying on the basement floor 
of crystalline rocks. This horizon has been well explored about Wash- 
ington and Alexandria, in most cases with great success, and was prob- 
ably reached by the 210-foot well at Quantico. South of Quantico for 
some distance it does not appear to have been reached by any of the 
wells except one (at 315 feet) at Walkerton, on the Mattapony River; 
but from the general character of the formation as exhibited in its 
outcrops, and its productiveness of water northward, I have reason to 
believe that it is a great water bearer throughout a wide extent. Its 
general relations are shown in the sections in PI. XVI. How far east- 
ward the coarse materials extend in the basal beds of the Potomac 
formation is not known, for they lie deeper than any of the wells appear 
to have penetrated. The North Point well is reported to have reached 
a granite" and found no water supply in the basal beds, but, as I have 
elsewhere explained, the record and conduct of this well do not afford 
conclusive evidence either of the actual absence of water or of the 
presence of granite at the bottom of the boring. The well no doubt 
reached the Potomac formation, and it may have penetrated far into it. 
The water at the Chamberlain Hotel at Fort Monroe is thought to be 
from upper Potomac or possibly Magothy beds, but the evidence is not 
conclusive as to the precise horizon. 
Water occurs at various horizons in the Potomac formation above 
the basal beds, in sands intercalated among the clays. This water is 
an important source of supply in the District of Columbia, and it also 
affords a large yield at the well at Barrow, near Quantico. Only one 
of the wells south of Fredericksburg has penetrated to these waters — 
the one at Walkerton at a depth of 315 feet — so that their southeastern 
extension has not been well explored, but there is a fair possibility of 
finding one or more of them in that region. The 600-foot boring at 
