underlying hard rock. Outside of the towns, if care is taken to locate wells so that they will not receive drainage from outhouses or barnyards, the water is potable. Shallow wells are always dangerous, however, in even small centers of population since it is practically impossible to prevent contamination.

MONTGOMERY COUNTY

The surface features of Montgomery County are similar in character to those of the adjoining county of Howard and the other Maryland counties along the eastern border of the Piedmont. The surface is a much dissected, rolling upland, ranging in elevation from between 200 and 300 feet along the eastern border to over 800 feet in the northern part of the county where Parr's Ridge enters the county from the northeast and gradually sinks to the general level of the western part of the county which is between 400 and 500 feet.

From Seneca to the bend of the Potomac at the mouth of the Monocacy the country is underlain by the sandstones of the Newark formation, and this area is both flatter and lower than elsewhere in the county and seldom reaches 400 feet.

GEOLOGY

The unconsolidated sands and clays of the Lower Cretaceous cover disconnected areas along the eastern border of the county adjoining Prince George's County. The western part of the county from Seneca to the Frederick boundary on the Potomac is underlain by the red and gray sandstones and shales of the Newark formation of Triassic age. Elsewhere and including the major portion of the county the underlying rocks beneath the surface mantle of soil are granites, gneisses, serpentine, and basic and acid volcanic rocks of great age and highly crystalline. These are much crumpled, and while underground waters are plentifully stored in joints and fault planes, they occur in no regular or predictable position, and it is therefore impossible to predict the artesian prospects for areas of this kind.

SURFACE WATERS

The surface streams are small and subject to great seasonal variation. All are liable to surface contamination and should not be utilized for domestic or municipal supplies, except where they are subject to scientific filtration. The two larger streams are the Patuxent, which forms the Howard boundary, and the Potomac, which forms the southern boundary. The latter carries large amounts of water and develops extensive water power at Great Falls and elsewhere in the county. The former is utilized to some extent for water power and small developments are utilized for milling operations on various small streams throughout the county. The public supply of Washington is taken from the Potomac at Great Falls.

UNDERGROUND WATERS

Artesian Waters

There are no large centers of population or manufacturing enterprises requiring large amounts of water, so that throughout much of the county the inhabitants utilize springs and shallow dug wells for domestic purposes. The number of artesian wells that have been put down is small and none reach great depths. The yield and head vary through wide

This well fluctuated with wet and dry seasons. It was a dug well 70 feet deep. Afterward an attempt was made to get more water by drilling deeper. Drilled to 180 feet with no

increase.

limits from place to place. An 87-foot well at Barnesville pumps 100 gallons per minute and heads 25 feet below the surface.

The National Park Seminary at Forest Glen has two 6-inch wells, 287 and 300 feet deep, each yielding 11 gallons per minute. The municipality of Rockville with a daily consumption of 40,000 gallons obtains its supply from three wells, 225 to 290 feet deep.

A list of the wells of the county and such additional data as is available are given in the appended table and require no special discussion.

Non-Artesian Waters

SPRINGS.-Springs are abundant and well distributed throughout the county, and are frequently untilized for domestic purposes throughout the rural districts. The waters of Carroll Springs at Forest Glen are sold as table water in Washington.

SHALLOW WELLS.-Dug wells are commonly utilized for domestic supplies throughout the county, being usually dug down until the water which lies above the surface of the underlying unweathered rocks is reached. Such wells are sanitary throughout the thinly settled districts if they are located far enough away from outhouses and farm yards to prevent contamination. Such shallow wells in small towns are always liable to contamination and their use is not to be recommended.

FREDERICK COUNTY

Frederick County includes several different types of country. On the east are the series of minor ridges culminating in Parr's Ridge, made up of intensely folded and crumpled schists and gneisses, and with narrow valleys and heights of 500 to 600 feet: A remnant of the ancient highlands preserved from erosion by the hardness of the quartzite of which it is composed is Sugar Loaf Mountain in the southernmost corner of the county which reaches an elevation of 1281 feet. West of this is the broad and relatively level surface of the Frederick or Monocacy Valley with elevations of from 200 to 300 feet. The valley is bounded on the west by the rugged Catoctin Mountain which increases in elevation from about

1000 feet on the south to between 1600 and 1700 feet on the north and forms the line of division between the Piedmont type of country to the east and the Appalachian type of country to the west.

The country between Catoctin Mountain and the Blue Ridge, whose even-topped summit at an average elevation of about 2000 feet constitutes. the western boundary of the county, is a rugged upland, particularly toward the north, where it is about 700 feet in elevation, declining farther to the north where it is about 500 feet and also becoming lower toward the Potomac.

That part of the county east of the Frederick Valley is underlain by the intensely folded, ancient crystalline rocks, including some gneiss and marble and a complex of acid and basic rocks partly volcanic and partly sedimentary in origin, the whole metamorphosed into schists. Toward the valley are narrow dikes of diabase, a dark, igneous rock here of Triassic age.

The Frederick Valley is underlain by the folded and faulted formations of the Shenandoah limestone (Cambrian and Ordovician) and by the