The major portion of this section is referred to the Patuxent (the Arundel is not recognized), while the beds from 42 to 112 feet are identified as Patapsco. Whether or not this well is drawing from the base of the Patuxent is not known for certain, but the mention of sand and gravel as the base of the section together with the great thickness forces the conclusion that this well has almost reached the crystalline floor. In the Patuxent folio' underground water contours are given that would place the basal Potomac waters much farther down in this well. If, however, consideration is given to the straightening of the strike to a more nearly north and south direction which is noticeable in the Potomac Valley and which is finally achieved in Virginia, the base of the Patuxent should be found at some such depth as that of the Indian Head well.

The first of the government wells at Indian Head, the one given above, was about 100 feet above tide and did not flow, but the later ones have been drilled nearer to water level and have achieved varying flows.

Charles County, then, is underlain by the Eocene horizon, by the Magothy and by the Patuxent waters. The Patuxent probably lies at a depth of from 1200 to 1400 feet along a line drawn through Waldorf and La Plata and will rise or sink at the rate of about 60 feet to the mile, according as distances are taken either to the northwestward or southeastward of this line.

The Eocene water will probably continue to be the objective of most of the future wells of this county and should be reached at moderate depths over its entire distribution, but will yield flows only on low land within 25 feet of tide level.

Non-Artesian Waters

SPRINGS.-In no part of the Coastal Plain are springs more numerous than in Calvert, Charles, and St. Mary's County, and Charles has probably more than either of the other two. Good springs are frequent, but only a few of them are utilized because it is usually more convenient to obtain water from wells located near the houses. The springs are fed mostly

1

Geologic Atlas No. 182, U. S. Geological Survey, 1907.

by the water absorbed from rainfall by the surficial sands, through which it sinks until its downward movement is stopped by marls or clays. The point of emergence is on the slopes or in the ravines which are cut into the surface of the Pleistocene terraces. While most of the springs issue from sands of Pleistocene age not infrequently the Miocene sands near the surface are trenched by the streams and furnish good springs.

The volume of flow is seldom large, though most of the springs will supply a single household and many of them would furnish enough water for several families. Some of the weaker flows from the Pleistocene formations fail in extremely dry weather, but many of the stronger springs are not materially affected by drouths, the springs from the Miocene formations, for example, usually having a fairly constant flow. The spring water is usually free from organic and inorganic impurities. Locally where springs emerge from thin beds of Pleistocene sand they may receive some water containing organic matter of a more or less deleterious character, but most of the water from the Pleistocene formations and practically all of that from the Miocene formations is free from such contamination. The percentage of inorganic matter in solution in the spring water is commonly so low that the supplies are soft, but locally there is enough mineral matter in solution to make the water slightly hard. Some of the springs from the Pleistocene formations supply water containing iron, dissolved from deposits in the sands, but the quantity is seldom large enough to interfere with the use of the water.

SHALLOW WELLS.-Dug, driven, or even drilled shallow wells supply most of the water used for domestic purposes in Charles County. The amount of relief and the presence of sands of Pleistocene and Miocene age which form the surface of the county all contribute to the ease of reaching a fairly constant supply of good water. The wells vary in depth from 15 to 40 feet. Locally, wells are deeper, reaching a depth of 80 feet, as at Allens Fresh, although this well probably should be classed as artesian since the water is under a slight head. As a matter of fact, a good many of the wells on the uplands are down into the Miocene, but the dissection is so great as to prevent storage and so inhibits flows or even large heads.

The quality of the water furnished by shallow wells is usually very good, but local conditions easily affect their purity. Bryantown, for instance, had an epidemic of typhoid fever several years ago because the town is situated on the side of a hill and downward drainage was constantly polluting the lower wells. The well on the top of the hill was the only one that failed to show the danger signal, Bacillus coli.

The need of locating wells so that they will be in no danger of sewage pollution is an elementary lesson in sanitation and has been iterated and reiterated in every publication concerned with public health. If the wells cannot be removed from danger of seepage drainage they should be sunk to below a continuous impervious bed, typified in this region by clay. Besides harmful organic matter the water sometimes contains less harmful but more disagreeable substances, usually in the form of decayed vegetable matter deposited with the sands. While this cannot be excluded from the water it is seldom harmful, and unless the water is rendered unpalatable its presence can usually be disregarded.

Inorganic matter is frequently present in the shallow water, the most noticeable element being iron, which is sometimes present in objectionable quantities, staining clothes and forming a scum on the surface of standing water. Iron is very irregularly distributed in the shallow wells, so irregularly that only a part of the wells in a given community may show its presence, although they all are of the same depth. The mineral is dissolved by the water in its passage from the sands and gravels of the Pleistocene which are frequently coated with iron and locally composed of iron crusts or nodules.

CALVERT COUNTY

Calvert County lies wholly within the Coastal Plain province. The relief is slight and the former level surface has been dissected by streams to form the present rolling upland made up of three terrace plains ranging from sea level, in the case of the lowest, to about 180 feet in the case of the highest, which forms the main divide of the county.