Abstract Cambrian carbonate rocks in the central Appalachian region were deposited both on an extensive carbonate shelf and in a deeper water slope and basin which was generally east of the shelf. Modern sedimentary environments provide analogues for specific parts of the shelf carbonate rocks and to a lesser extent for the basinal carbonate rocks. The deeper water carbonate rocks are composed of thin-bedded micritic limestone and thickly to massively bedded peloidal limestone and breccia. These rocks result primarily from clastic deposition of shelf-derived material. Evidence for subaqueous slumps and debris flows is present in the composition and stratification of the coarse-grained limestone. Centimeter-thick argillaceous limestone beds are graded and in rare cases contain complete Bouma cycles; these suggest deposition by turbidity currents. Relative amounts of biogenic debris, bioturbation, and vertical variability of sedimentary structures are qualitative bathymetric indicators. Stratigraphic proximity to shoal-water carbonate rocks and the thickness of slope deposits suggest that water depths were as great as 500 meters in the basin. Erosive structures ranging from tidal channels to submarine canyons are local features at or near the carbonate shelf margin. The composition and organization of breccia deposits and surrounding rocks in the Shady Dolomite (Lower and Middle Cambrian) near Austinville, Virginia, in the Kinzers Formation (Lower and Middle Cambrian) near Thomasville, Pennsylvania, and in the Frederick Limestone (Upper Cambrian) near Frederick, Maryland, represent three distinct deeper water environments adjacent to the Cambrian carbonate shelf. The shelf and basin in the Frederick and possibly the Austinville areas were connected by a carbonate depositional slope which extended seaward at a very low angle from mean sea level to depths of 500 m or more. Near York the shelf margin was highly dissected in at least one area and higher angle slopes persisted from Early to Middle Cambrian time.

Abstract Lead has been a much-sought-after commodity in North America since early Colonial times. Although more sophisticated uses, such as in pipes and vessels in water systems, coins, pottery glaze, and roofing, were common in Babylonian, Egyptian, and Roman cultures, the principal need for lead on the American frontier was to make bullets. Military success in the frontier wars and in the Civil War was affected by the ready availability, or lack, of ammunition. Hence, as the population moved westward from the Atlantic seaboard and spread along the Ohio and Mississippi River systems from New Orleans, localities where lead mineralization cropped out soon attracted attention and became population centers. The Wisconsin-Illinois District (discovered in 1682), southeast Missouri (1720), Austinville, Virginia (1750), and Rosiclaire, Illinois (1830), are notable examples. There were also numerous showings that never developed into large producers. Early discovery of lead deposits was facilitated by the fact that galena, the most common lead mineral, is resistant to weathering and persists in the clayey residuum. In southeast Missouri, the greatest North American lead-producing region, all of the production for the first 150 years was from such residuum rather than from solid rock. Plate 1C shows the locations of the deposits that have produced over 95 percent of all the lead mined to date in the United States. The productive longevity of some of the early-found eastern deposits is truly remarkable. Ammunition is still a significant use for lead, but since the beginning of the Industrial Revolution in the 19th century,