This well shows an extraordinary thickness for Lower Cretaceous deposits at a point near where they have been thought to thin out. An obvious and probably the correct explanation is that this well is located along an old stream channel, that of the pre-Cretaceous Potomac. The Potomac above the fall line is an ancient stream, post-Triassic and preCretaceous in its present form, but probably already defined, although poorly, during the Triassic elevation. Back in the Piedmont province the bed of the Potomac is 300 to 400 feet below the surface of the country 3 or 4 miles in from the banks and so, even though the valley of the ancient Potomac was not quite so deep as at present, a transgressing sea such as that which deposited the Patuxent sands would fill in this valley in an attempt to make a regular and even coast line.

Non-Artesian Waters

SPRINGS. There are a large number of springs in Prince George's County, and while none of them is very large they will usually furnish enough water for a single household or farm. The springs are usually situated on the sides of the valleys or at the head of small depressions in some of the terraces which form the surface of the country. In general, they are but little used because they are not always convenient to houses. The flow seldom exceeds 4 or 5 gallons per minute, and many of the springs are scarcely more than mere seeps from the surface sands. There is a general fluctuation of volume due to variations in the amount of rainfall, and a few of the springs from surficial sources cease flowing during very dry weather. In contrast to this general rule, a few of them are not affected by changes in precipitation, but maintain their volume practically unchanged during both wet and dry seasons. The water in these springs may be from either Pleistocene or older sands. Springs from the Pleistocene sands are more numerous but their flow is usually affected by seasonal changes. The water from most of the springs is pure, being remarkably free from both organic and inorganic impurities, although locally where springs are supplied from the Pleistocene sands the water may become contaminated by organic matter from the surface, but fortunately this condition is uncommon.

More commonly the foreign matter is inorganic material dissolved from the substances contained in the water-bearing sands. One of the most common is iron obtained from nodules and boulders containing this element imbedded in the water-bearing sands. The other substances are those common to ordinary ground waters and their presence in some of the water makes it slightly hard. Water from some of the springs near Washington has an extensive sale, but this is chiefly as drinking water. At various times efforts have been made to develop mineral springs but they have not been very successful. Among the springs thus exploited was the Bladensburg Spa which furnishes a water high in iron.

The following analysis of the water from the Bladensburg spring is incomplete but will show the essential constituents:

SHALLOW WELLS.-The shallow wells of Prince George's County are, naturally, the commonest, since there are few manufacturing plants or canneries, and of the communities requiring municipal supplies several are within reach of surface supplies that can be utilized. The varied surface geology of Prince George's County and the topographic dissection renders shallow wells a valuable source of water in small quantities.

The dug wells are frequently not over 10 or 15 feet deep and the general range of shallow wells seldom exceeds 20 to 40 feet. The shallowest wells are those located on low ground near the level of the large bodies. of surface water. As one ascends to the uplands the wells usually become

progressively deeper, though there are local exceptions to this general rule where water-bearing sands lie near the surface. This condition is most commonly found on the broad areas of nearly flat terraces, though it is sometimes found on the slopes. The deepest wells are located on high hills where permanent supplies can only be obtained by sinking the wells to sands or gravels overlain by heavy beds of clay and marl.

Many of the shallow wells obtain water from some of the formations of Pleistocene age that form the terraces. On the lower terraces the shallow wells usually obtain their supplies within the Talbot formation, but on the higher terraces the deeper wells often penetrate to the older geological formations, although the Brandywine, through its wide extent, will furnish water from its base.

The quantity of water in the shallow wells is seldom large, amounting in most wells to less than 10 feet and in many to only 3 or 4 feet. Some of the wells that obtain water from the surficial sands are affected by the amount of rainfall, and the quantity of water varies from several feet during rainy seasons to little or none during droughts. In the deeper wells there is less variation in quantity of water, the level remaining relatively constant despite the change in amount of rainfall. Even after making allowance for variations it is usually possible to obtain large enough supplies from shallow wells to meet all the demands of the rural population.

The quality of the water from shallow wells varies with the depth and location of the well, and there are local differences which appear to be independent of depth and location. The quantity of organic matter is controlled by local conditions. In some places the water-bearing beds contain decaying vegetation which gives the water a disagreeable odor and may also affect the taste. This condition is most common in the Talbot formation, but it has also been noted in some of the other horizons. Very shallow wells or those improperly cased may receive organic matter by the entrance of contaminated surface water, but fortunately this condition may be remedied by properly and tightly casing the well or by sinking the well to water-bearing sands or gravels covered by impervious clays or marls, and then inserting water-tight casings. The amount and

character of the inorganic matter in water from shallow wells is controlled by the nature of the soluble materials in the water-bearing beds and the opportunities for solution. The most common substances are those present in nearly all ground water, such as lime, magnesia, iron, etc. These substances make the water hard and the iron is especially annoying because it forms a red or yellow deposit when the water is exposed to the air or boiled. Iron is found in much of the shallow well water, especially since there are nodules or boulders of the ore abundantly scattered through the Pleistocene sands and gravels.

CHARLES COUNTY

Charles County lies wholly within the Coastal Plain of Southern Maryland. Much of the country lies at a considerable elevation above tide for a Southern Maryland county, and the surface, originally flat terrace plains, is now much dissected by the network of minor streams, only the flat-topped divides preserving the original level surface.

The major elevations of these divides gradually increase toward the north and northwest from 100 feet on Cobbs Neck in the southern part of the county to 180 to 220 feet near the Prince George's County boundary.

The geological formations exposed in the county range in age from the Lower Cretaceous to the Pleistocene. The former are exposed in a narrow belt along the Potomac in the northwestern part of the county,