Reports
Physical properties of nonmarine Cretaceous clays in the Maryland Coastal Plain
1961, Knechtel, M.M., Hamlin, H.P., Hosterman, J.W., and Carroll, D.
Bulletin 23
Introduction
Argillaceous materials in nonmarine sedimentary strata of Cretaceous age in the Maryland Coastal Plain have been investigated in pursuance of cooperative agreements between the Maryland Department of Geology, Mines and Water Resources and two agencies of the United States Department of the Interior: the Geological Survey and the Bureau of Mines. Listed in tables 1 to 5 are data relating to the geology, mineralogy, chemistry, and potential uses of sampled clay-bearing materials typical of the nonmarine strata, as well as a few materials associated with underlying pre-Cretaceous crystalline rocks and superjacent marine Cretaceous strata. The localities listed in the tables are marked on Plates 1 to 5, which also show areas wherein the crystalline rocks, nonmarine strata and marine strata are exposed; profiles on each of these plates give a general impression of the geologic structure, stratigraphic relations, and overall thickness of the nonmarine strata.
The areas shown lie partly on the Atlantic Coastal Plain and partly within the Piedmont physiographic province (fig. 1). The two provinces are separated by a somewhat vaguely defined transitional belt averaging about 5 miles in width, known as the "Fall Zone" or "Fall Line", which extends in a northeasterly direction across the State. The bedrock deposits are extensively concealed by soil and alluvium. They have been logged in many water wells but are readily visible at the surface only in small exposures along streams and in excavations such as road cuts, gravel and clay pits and abandoned iron ore workings.
Virtually all the types of material exposed or logged are believed to be represented among the samples collected for study. Those from a few of the localities listed in column 1 in Tables 1 to 5, came from surface exposures; all the rest were taken from exploratory holes, most of which were about 100 feet deep. The holes were bored with a truck-mounted 5-inch auger. Most of the holes were bored close to lines laid out nearly normal to the strike of the Cretaceous rocks (for example, Pl. 1, lines 1, 2, and 3). The holes were spaced with a view to exploring stratigraphic intervals encompassing the entire thickness of the nonmarine Cretaceous sequence. The positions of the holes, as projected along the lines, are indicated in the geologic profiles on Plates 1 to 5; the materials brought to the surface by the auger or measured in surface exposures are logged under heading 2 of Tables 1 to 5.
