136 ARTESIAN WELLS ON THE ATLANTIC COAST. [bull, m 
Solomons Island, Calvert County. — There are four flowing wells on 
this island, and another at Eousby on the mainland just north. They 
average about 250 feet in depth and furnish good supplies of excellent 
water. The water horizon is the basal Chesapeake beds, the same as 
in the St. Mary County wells, and at Denton and Cambridge on the 
Eastern shore. 
St. Mary County. — The wells at Leonard town, Piney Point, St. George 
Island, and about St. Inigoes are all sunk to the basal Chesapeake 
horizon, which furnishes water in the group of wells across the river 
in Yirginia. The relations of all these wells are shown in section 1, 
PL XII. 
Chapel Point, Charles County. — This place is on Port Tobacco River, 
near its mouth. The well is 237 feet deep, and is said to have a large 
water supply which rises to near the surface. The record, unfortu- 
nately, could not be obtained. It is probable that the water horizon is 
at the base of the Pamunkey formation, or the same as in the deeper 
wells at Colonial Beach, across in Yirginia. 
THE BALTIMORE REGION. 
GEOLOGY OF BALTIMORE. 
Baltimore lies in the zone in which the crystalline rocks emerge from 
beneath the Coastal Plain deposits. Although the greater part of the 
city is built on the Potomac formation, the depressions of Jones and 
Gwynns falls are excavated to the crystalline rocks, and these rocks 
rise rapidly to constitute the surface in the region north and west. 
The Potomac formation consists of its usual materials, in which pre- 
dominate clays of various colors and fine sands. Toward its base 
there are intercalated beds of coarse sands and gravels, and at the base 
an almost general occurrence of these materials, lying on a floor of 
crystalline rocks. Some features and relations of these basal beds 
are shown in Pi. IX. The coarse materials contain widely extended 
sheets of water, which have been tapped by many well borings of mod- 
erate depth. The rock floor slopes quite steeply eastward, at a rate 
averaging about 65 feet per mile, but the rate appears to increase 
locally to 100 feet along by the Basin. The basal gravels pass beneath 
tide water along a line extending from the lower Baltimore and Ohio 
Kailroad bridge over Gwynns Falls to the Fayette street bridge over 
Jones Falls, and thence due east-northeastward, as shown by tne blue 
zero line on the map, PI. VII. The principal water supplies are to 
the south of this line, for to the northward the waters are free to flow 
laterally into the depression of Jones and Gwynns falls. The basal 
gravels emerge in the northern portion of the city, although in some 
areas they are overlain by a thin cap of gravels and loams of earlier 
Columbia age. They cap the Druid Hill Park region, the ridges for 
some distance out Charles street, Roland avenue, and York, Harford, 
