3 gallons per minute; at Leonardtown, St. Mary's County, where wells 270 feet in depth flow 10 gallons per minute; at Easton, Talbot County, where wells 115 feet deep yield 30 gallons per minute by pumping; at Denton, Caroline County, where wells 180 feet deep flow 10 gallons per minute and supply 40 gallons per minute by pumping; and at Federalsburg, Caroline County, where wells 265 feet in depth flow 20 gallons per minute and furnish by pumping 40 gallons per minute.

Quality. Uniformly good, slightly hard, at times containing in solution a greater or less amount of alkaline earths.

WATER FROM THE UPPER MIOCENE DEPOSITS

Water may be secured from Upper Miocene deposits at depths of less than 250 feet only in the extreme southeastern portion of the state on the Eastern Shore.

ST. MARY'S FORMATION.-The best known water-bearing horizon in the Upper Miocene is at the base of the St. Mary's formation, but water may come in part from the upper beds of the Choptank formation below. It occurs in a belt about 30 miles in width.

Thick and prevailingly sandy beds of late Tertiary age are found on top of the St. Mary's formation in southern Delaware and in Wicomico, Somerset, and Worcester counties, Maryland. These sands have already been referred to in the account of the geology as representing either the Cohansey formation of New Jersey or the Yorktown formation of Virginia. They are frequently but irregularly water-bearing, so that there is a wide belt of country on the Eastern Shore southeast of a sinuous line drawn from Dover, Delaware, to Cambridge, Maryland, where waters in the upper Miocene are likely to be encountered within 100 feet below tide as shown on the accompanying map (Fig. 89). These later horizons are, however, much less persistent than those of the older Coastal Plain formations, and in parts of the area mapped they appear to be entirely wanting. Depth.-From 90 to 250 feet.

Static Head.-From several feet below to 10 feet above the surface; usually flowing; easily pumped by suction.

FIG. 89.-MAP SHOWING UPPER MIOCENE WATERS.

0-0-Line where the base of the upper Miocene passes below tide level.

A-A-Line northwest of which various small water horizons of the upper Miocene may be encountered within 100 feet below tide level.

Quantity.-Large and small. Among the wells which derive their supply from this horizon may be mentioned the following: Several wells at Whitehaven, Wicomico County, 95 feet deep, which flow 10 gallons per minute; wells at Salisbury, Wicomico County, 90 feet in depth, which yield 30 gallons per minute by pumping; wells at Crisfield, Somerset County, 225 feet deep, which supply 30 gallons per minute by pumping; and wells at Snow Hill, Worcester County, 267 feet deep, from which 70 gallons per minute are pumped. Other wells of larger capacity are those at Ocean City, Worcester County, 250 feet in depth, which flow 30 gallons per minute and yield 100 gallons per minute by pumping; at Pocomoke City, Worcester County, where a well 247 feet in depth flows 40 gallons per minute and yields 175 gallons per minute by pumping. This latter well struck higher water horizons in the St. Mary's formation, first at 120 feet, where 60 gallons per minute could be pumped, and another of salt water at 225 feet, which yielded 100 gallons per minute. by pumping.

Quality. Good, usually alkaline with varying amounts of iron.

WATER FROM THE PLEISTOCENE DEPOSITS

Water is obtainable rather generally throughout the Coastal Plain at the base of the blanket of Pleistocene formations. The supplies, however, are for the most part small, the more important being found at the base of the Wicomico and Talbot formations; the latter, the latest of the geological formations of the state, forms a low terrace adjoining the tide waters and is therefore frequently invaded for considerable distances by the salt and brackish waters. It is for this reason usually unpotable, or at least unpalatable, and is easily liable because of the poor surface drainage to become contaminated. The Wicomico formation which occurs at a somewhat higher level is not subject to the same deleterious effects as the Talbot formation, and the same is likewise true of the still higher terrace deposits of earlier Pleistocene age, but because of their limited area of extent they are of relatively small importance as water horizons. Their higher elevation likewise renders them less stable as receptacles for a permanent natural supply, and they will not be further considered in this discussion.

Depth.-From 8 feet in the wells of the Talbot formation to 45 feet in the deeper wells of the Wicomico formation.

Static Head.-Generally from 3 to 5 feet, closely dependent on the rainfall, the level of the water in the well being the same as the top of the ground water; never flowing; pumped by hand or suction pumps.

Quantity. Small. The quantity of water derived from Pleistocene wells is always small, probably never more than a few gallons per minute. The supply of water in all wells is exhausted in less than an hour's steady pumping.

Quality. Generally poor, usually high in iron, and salty near borders of salt or brackish water; very liable to surface contamination.

UNDERGROUND WATERS OF CENTRAL MARYLAND

The underground waters of Central Maryland are derived chiefly from shallow wells, except in proximity to the larger municipalities where wells of greater depth are not uncommon. This is especially true of the region about Baltimore.

The underground waters come from (a) shallow wells that do not reach below broken and oftentimes disintegrated materials of the upper portions of the underlying rocks, generally less than 60 feet in depth, and (b) from deeper well borings that cut the water fissures of the solid rock generally at depths of from 50 to 350 feet. The former are meteoric or rain waters that are easily subject to contamination, while the latter are deepseated waters that through hydrostatic pressure have generally come from long distances and are rarely if ever contaminated. The quality of these waters is also dependent on the mineralogical composition of the rocks, of which four general types may be recognized: (1) Calcareous or calcareous-magnesian rocks, (2) siliceous rocks, (3) iron-magnesian rocks, and (4) aluminous rocks.

WATER FROM CALCAREOUS AND CALCAREOUS-MAGNESIAN ROCKS

(LIMESTONES, MAGNESIAN-LIMESTONES, MARBLES, ETC.)

Water is widely found in the calcareous and calcareous-magnesian rocks of the central area. These rocks occur in more or less isolated patches in

the eastern part of the district, but in the western part of the area are found as broad belts extending from north to south across the state.

Depth.-50 to 300 feet, although a few wells of greater depth have been sunk.

Static Head.-Generally from about 40 feet below to a few feet above the surface; with few exceptions are non-flowing; generally pumped.

Quantity.-Large to small, A few wells are found in the marble belts to the north and northwest of Baltimore in Baltimore County. At Lutherville a well 140 feet deep with a head near the surface yields 12 gallons per minute by pumping; another well nearby, 125 feet in depth with a head 15 feet beneath the surface, yields 70 gallons per minute; a short distance farther north, at Timonium, a well 159 feet, which heads nears the surface, yields 30 gallons per minute. In the Green Spring Valley a well 113 feet in depth with a head 18 feet beneath the surface yields 56 gallons per minute.

At Clarksville, Howard County, to the southwest of Baltimore, a well 30 feet in depth with a head 26 feet beneath the surface yields 12 gallons per minute.

A number of wells are found in the isolated limestone areas of Carroll County, among them a well at Westminster 90 feet in depth with a head 14 feet beneath the surface which yields 50 gallons per minute; and another at the same place, 70 feet in depth with a head 27 feet beneath the surface, yields 35 gallons per minute; at Uniontown a well 25 feet in depth, which heads 10 feet beneath the surface, yields a small supply; at Union Bridge a number of wells in the limestone yield variable supplies, some very large, among them are three adjacent wells 50 feet in depth with a head 12 feet beneath the surface which yield 50 gallons per minute; another well 170 feet deep with a head of 13 feet yields 400 gallons per minute; another 214 feet deep with a head 12 feet beneath the surface yields 50 gallons per minute; another 246 feet in depth with a head 12 feet beneath the surface yields 50 gallons per minute, and still another 464 feet deep with a head 12 feet beneath the surface yields 300 gallons per minute.