Miocene deposits flows along this contact until it is tapped by some valley slope. Because of the thinness of these Pleistocene deposits the springs are less numerous in Calvert than in the other counties of Southern Maryland and they frequently fail in dry seasons. The spring water is frequently charged with iron and because of the danger of contamination from surface drainage should not usually be depended upon for domestic use.

SHALLOW WELLS.-The majority of the inhabitants, living as they do along the divides where run the roads, depend upon shallow wells for water. Most of the shallow wells draw from Pleistocene sands, which are relatively thin in this county so that the wells are correspondingly shallow. The range in depth of the Pleistocene wells is from about 15 to 45 feet. There are a good many wells in the county that are sunk to about 60 to 90 feet and find water in the upper beds of the Miocene formation which lies nearest to the surface at the particular locality. These wells are scattered over the whole county irrespective of any particular stratigraphic level and are usually very close to the catchment area of the sand and so have rather low heads, but the improved quality of the water and the greater reliability of supply are very great advantages over the shallower Pleistocene wells.

ST. MARY'S COUNTY

St. Mary's, the southernmost county in Maryland, occupies the peninsula between the Potomac and Patuxent rivers and Chesapeake Bay. Its sur-. ficial deposits erode easily and its former level surface has been much dissected, resulting in a rolling topography. Four levels or terrace surfaces are recognizable. The lowest, lying between tide and 45 feet elevation, is known as the Talbot terrace plain, and is an almost unbroken flat over much of its extent. The second, known as the Wicomico plain, is somewhat more dissected, its surface rising toward the divides and lying between 55 and 80 feet above tide. The third, known as the Sunderland, forms the main divide of the county. It is much more dissected than the other two and its rolling surface rises toward the northwest to a height of about 180 feet. A fourth and older terrace plain, still more dissected

than the preceding, extends southeastward to the vicinity of Charlotte Hall and is known as the Brandywine plain.

The oldest deposits now exposed within St. Mary's County are three formations of the Chesapeake group of Miocene age. They are, from oldest to youngest, the Calvert, Choptank, and St. Mary's formations. These consist of sands, clays, and marls. Beneath the Miocene but nowhere exposed in the county is the Eocene. The Eocene and the Calvert formation of the Miocene underlie the whole county and are the source of abundant underground water. Overlying the Miocene are the sands, loams, clays, and gravels of the four surficial formations, the Brandywine, Sunderland, Wicomico, and Talbot, which lie at successively lower levels and form the terrace plains previously mentioned.

SURFACE WATERS

St. Mary's County is almost entirely surrounded by water, but in the absence of large towns or extensive industries requiring large amounts of water the streams are not utilized as sources of supply. Patuxent River

forming the northeastern boundary, Potomac River forming the southern boundary, and Wicomico River forming part of the western boundary are all tidal and consequently are brackish. The most important streams entirely within the county are Chaptico Creek, McIntosh Run, St. Clement and St. Mary's rivers. In addition to these four small rivers, there are many smaller creeks along the coast, all of which have the same general characteristics. Their basins are small and flat with considerable length of tidal flow. No water power is now utilized in the county, although at one time a small power plant on St. Mary's River at Clements was used for milling. Chaptico Creek has a drainage area of 32 square miles. The effects of the tide are apparent to just above Chaptico. The discharge, measured in 1904, about mile above Chaptico bridge was 12 second-feet.

St. Clement River has a drainage area of 23 square miles and is marshy toward its mouth. Its discharge is about 6.6 second-feet. McIntosh Run has a drainage area of 26 square miles and a discharge of 4.7 second-feet measured about 1 mile above Leonardtown. None of the streams of the county should be utilized for potable water since all are very liable to contamination and contain much vegetable matter in suspension.

UNDERGROUND WATERS

Artesian Waters

Many artesian wells have been drilled in recent years, particularly in the low-lying areas adjacent to the Patuxent and Potomac rivers. The water zones reached in these wells are of wide extent and their depths below the surface can be predicted with reasonable certainty for any locality in the county.

Two principal water horizons are known, one in the Calvert formation of the Miocene and the other and deeper one in the underlying Eocene.

Wells are down into the Calvert and the Nanjemoy, although the horizon called Nanjemoy is more probably the upper part of the Aquia, but in order to distinguish between the water at the base of the Aquia the upper level is called Nanjemoy. The Calvert is the main water horizon

and has been encountered under good heads from Leonardtown southeastward. At Leonardtown the water in the Calvert formation has been found at 195 feet in a well, the samples of which were described by N. H. Darton as follows:

It has been impossible to identify this well with any of those reported from Leonardtown, so it is not known whether this is a partial record of one of the deeper wells recorded in the appended table. A record of a well drilled by Mr. L. Rude in 1909 and compiled by him is as follows:

The wells at Leonardtown 260 feet deep do not have their casings extended all the way to the bottom, so that it is impossible to tell whether they are drawing from the basal bed of the Calvert as does the well at Wallville in Calvert County, but it seems likely that they do since they probably extend all the way through the 60 or 70 feet of water-bearing beds at the base of the formation.

The water in the beds at the base of the Calvert formation supplies the wells at Blakistone Island 156 feet deep, Leonardtown, Sotterly, along the beach near Millstone Landing and Pearson, Great Mills, Valley Lee, Piney Point, St. George's Island, the 277-foot well at Portobello, St. Inigoes, Drayden, and Cornfield Harbor. The Calvert water is first reached about 60 to 70 feet above the base of the formation, and in some