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Pedomorphosis revisited: Thyroid hormone receptors are functional in Necturus maculosus. Evolution and Development, 8(3), 284 292. ˇ Polak, S., Verovnik, R., Zakˇsek, V., & Sket, B. Trontelj, P., Goriˇcki, S., (2007). Age estimates for some subterranean taxa and lineages in the Dinaric Karst. Acta Carsologica, 36, 183 189.

SALTPETRE MINING David A. Hubbard Jr. Virginia Speleological Survey and Virginia Department of Mines, Minerals and Energy

DEFINITIONS AND IMPORTANCE Historically, saltpetre is one of the most strategic of commodities. It occurs naturally in caves and rockshelters, but it is rare. A suite of related nitrates occurs in many caves. The mining and processing of cave nitrateenriched sediments is a relatively simple endeavor, although labor intensive. The tendency of these sediments to contain a suite of nitrates rather than just potassium nitrate is one reason the archaic spelling saltpetre is used in reference to the mining of cave nitrates and the caves in which they occur. This convention is followed throughout this article. The invention of gunpowder revolutionized weaponry and warfare. Gunpowder, also referred to as black powder, consisted of a mixture of saltpetre, sulfur, and charcoal. Although saltpetre was used in the preservation of meats, the greatest historic demand for saltpetre was during times of insurrection and war. Nowhere has the quest for saltpetre contributed to historic events more than in the United States, where this commodity contributed to both the formation of a country and almost its destruction. The mineral niter (synonym, saltpeter) is potassium nitrate (KNO3). Like many other nitrate compounds, niter is deliquescent; that is, it has a natural tendency to draw water to itself and dissolve into a solution. Although deliquescent minerals can absorb moisture from humid air, they occur naturally in sheltered locations under conditions of low humidity or during periods of reduced humidity. The deliquescent nature of saltpeter is the reason for the old warning of soldiers and frontiersmen, who depended on their firearms for survival, to “keep your powder dry!” Caves and rockshelters, also termed rockcastles, are locations where nitrates may accumulate. Analyses of cave sediments, which were mined historically for saltpetre, commonly reveal no nitrate minerals. The reason is that most of the classical saltpetre caves are in regions where the humidity typically is too high for niter and the even more deliquescent minerals nitromagnesite,

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Mg(NO3)2
6H2O, and nitrocalcite, Ca(NO3)2
4H2O, to crystallize into their solid mineral forms. Instead, the saltpetre-rich sediments, historically termed petre dirt, contain concentrated viscose nitrate solutions in the form of sediment moisture. Because nitrate minerals rarely crystallize in most of the known saltpetre caves, other clues to the accumulation of nitrates in cave sediments are important. In the absence of niter, the foremost evidence of significant nitrate concentrations in cave sediment is the presence of efflorescent crusts. These white or light-colored powdery crusts commonly are composed of a mixture of soluble salts and minerals, such as gypsum and calcite, that accumulate on cave sediment and rock surfaces as a result of evaporation. Efflorescent incrustations signify locations where periodic atmospheric conditions allow evaporation and the concentration of the minute amounts of dissolved solids in interstitial soil and rock moisture. Precipitation and concentration drive the wicking action of the dissolved solids through soil and rock pores from their respective remote sources. The sources of most saltpetre cave nitrates are the surface ecosystems overlying saltpetre caves. Recent microbiological work in caves and karst has shown that bacteria are important in cave development (speleogenesis) and in the development of the secondary cave mineral forms (speleothems) that were thought to be the result of physiochemical reactions (Taylor, 1999). The importance of nitrifying and other bacteria in the accumulation of efflorescent crusts and nitrate accumulations in sediments (petre dirt) is unknown but probably is not trivial.

SALTPETRE MINING The mineral niter (KNO3) is rarely found in caves, but when observed it occurs as clear to white lint-like fibers, acicular (needle-like) crystals, powder, crusts, coralloid, or flowstone forms. The most extensive form observed in saltpetre caves is the lint-like fibers that occur in dense carpets on bedrock walls (Fig. 1) and sediment-covered walls and floors. These niter fiber occurrences can be harvested with the use of a thin wooden spatula or paddle-like scraper, leaving little or no evidence of extraction. Such a wooden scraper was observed high on a Virginia saltpetre cave ledge before this author had observed an efflorescent niter occurrence. The majority of the documented saltpetre caves does not normally contain crystalline niter. At the humidities typically found in these caves, the deliquescent nitrate accumulations occur as viscose nitrate solutions in efflorescent crusts on rock and sediment

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of the effects of niter in the preservation of meat may predate gunpowder, no evidence is known that niter was extracted from caves for preservation of meat remote from caves. The importance of gunpowder in revolutionizing armed conflict resulted in intense periods of demand for niter. In addition to mining in rockshelters and caves, saltpetre was obtained from artificial niter beds and from soils collected under buildings. In Western societies, the earliest documented search for niter is the 1490 quest of Hans Breu for saltpetre in Sophienho¨hle (Sophie’s Cave) in Germany. The French Revolution and Napoleonic wars of Europe (1792 1815) and the Revolutionary (1775 1783), 1812 (1812 1815), and Civil (1861 1865) wars of North America were periods of intense demand for saltpetre. The written record of actual saltpetre mining processes is sparse, as is typical for many mundane tasks. The most extensive known distribution of saltpetre caves and the best-preserved evidence of mining can be found in the southeastern United States. Although the mining evidence in each saltpetre cave is as different as caves are from one another, similar patterns of marks, disturbances, and artifacts convey some information about basic mining and processing methodologies. Tangible evidence of saltpetre mining includes the principal physical evidence of wall and floor sediment removal, the secondary evidence of lighting and names and artifacts used in mining or as bracing that date to the mining era, evidence of simple sediment processing and separation of rocks and clay balls, and modified pathways and conveyances of miners and mined sediment. Nitrate processing evidence is important in distinguishing saltpetre mining from sediment extraction for other purposes and is discussed in the section on saltpetre processing.

(A)

Principal Physical Evidence of Mining

(B) FIGURE 1

(A) Fibrous form of the mineral saltpeter carpeting cave walls in a Virginia saltpetre cave (photograph by John C. Taylor; image width approximately 12 cm). (B) Fibrous form of the mineral saltpeter carpeting cave surfaces in a Virginia saltpetre cave; scale is in centimeters.

surfaces and within sediments and bedrock proximal to the cave. The earliest mining of saltpetre may have been in China, dating from the development of gunpowder approximately 1000 years ago. Although the discovery

Physical evidence of sediment removal includes tool marks, wall discolor marks of former sediment levels, and tunnels and pits within sediments. Tool marks on worked sediment faces are of wide- and narrowbladed tools. Sediment mining tool marks predating the 1860s are typically hoe-like and wide bladed (10 to 13 cm), while many of those of the American Civil War era are narrow bladed (5 to 7 cm) and attributed to mattocks. The blades of these tools were metal, and rarely were such tools left in caves, while pointed digging and prying sticks and paddle-like spatulas are more commonly found. Pick and mattock impact marks on rock walls may relate to efflorescent wall crust or sediment removal. The discoloration marks of old sediment levels on bedrock walls provide an

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indication of the thickness of mined nitrate-rich sediment. An important distinction is that not all sediment in a saltpetre cave is equally enriched or desirable. Slightly worked deposits of difficult to process clay sediments with well-preserved mattock marks and well-developed white efflorescent crusts are evidence that the difficulty in extracting nitrates from clay outweighs the effort. Similarly, pits and tunnels through thick sediments may indicate low yield deposits, which were partially exploited, but such excavations may have had more utility as passage and haulage routes.

Secondary Evidence of Mining Indirect evidence of mining includes soot stains above torch perches and the stubs of pine faggots (torches) at worked sediment faces and along welltraveled routes between entrance and mining areas. Rock piles in wall niches or backfilled in small passages are evidence of hand-sorting of rock from the sediment. Less common are piles of small rocks and clay balls from sieving near the site of sediment mining or near locations where sediment was transported in cloth or burlap sacks. The combination of old sediment level stains and names dating to the mining era stranded high on walls, as well as remote clusters of tally and torch marks, may differentiate periods of mining. Mining artifacts include pointed wooden digging and prying sticks, wooden scrapers, and wood hoops for holding sacks open during filling. Stone and wood bracing stabilize undermined large rocks in some saltpetre caves. In breakdown mazes, the use of rock for slab and ceiling stabilization may not be obvious. The breakup of rock slabs to access the underlying sediment has resulted in labor-intensive passage enlargement and rock walls and fills that may appear as having other significance. Other modified pathways and conveyances include cut steps in steep sediment banks, stone steps, wooden stairs, boardwalks, and plank ramps across chasms and canyons; various types of ladders; and windlasses. Perhaps the most rewarding evidence of saltpetre mining is the correlation of names etched into cave walls with written mine-era records of payrolls, equipment receipts, or saltpetre production or sales receipts. Such corroboration sometimes allows the matching of different historic cave names with present-day names as well as verification of the nature of the sediment mining.

SALTPETRE PROCESSING In some saltpetre caves, evidence of the processing is intermingled with the mining evidence. Large

hoppers or smaller vats were commonly used in saltpetre processing, but barrels and sections of hollow logs also were employed. Two of the best-preserved examples of sediment processing equipment are displayed on cave tours: rectangular hoppers in Mammoth Cave in Kentucky and V- or wedge-shaped vats in Organ Cave in West Virginia. Intact hoppers and vats are rare in most present-day saltpetre caves. All that remains in many saltpetre caves are the internal casts of nitrate-depleted mine spoils. Surrounding such casts occur the discarded piles of leached cave sediments, discarded from the vats prior to their last loads of sediment. The wooden remains of many hoppers and vats have rotted or been destroyed by vandals. Processing requires a source of water, which is not usually located close to the nitrate-rich cave sediments that require at least a periodic reduction in the humidity to accumulate. Processing of the majority of saltpetre cave sediment has entailed the puddling of the nitrate-rich sediments in a hopper or vat. After the nitrates are leached from the cave sediments, the liquid, termed beer, is decanted. To this beer another leachate, from wood ashes (potash), is added until a white precipitate ceases to form from the mixing of the two solutions. This process exchanges the potassium cation of the potash solution for the calcium and magnesium cations of the cave nitrate solution. The resulting potassium-rich nitrate solution is transported to large iron kettles for further processing and eventual fractional crystallization of the niter crystals. The kettles are usually hemispherical and without legs or other attachment points that would serve as heat sinks, resulting in differential heating within the kettle. Most kettles have a wide lip or rim by which they are supported over a heat source. The fractional crystallization process enables workers to selectively crystallize specific soluble salts, while leaving more soluble salts in solution. The processing of sediment, especially for smaller caves, occurred outside of many saltpetre caves for lack of a suitable water source. Some small caves were worked as satellite locations to a nearby major saltpetre works. No evidence of kettle processing is known from within any saltpetre cave, although kettles are known to have been hidden in and recovered from caves. Perhaps the most impressive examples of evidence of in-cave saltpetre processing are preserved at Mammoth Cave in Kentucky. Some of these War of 1812 era workings may be observed on tours and include large hoppers and a complex system of hollow log plumbing, whereby freshwater was pumped into and saltpetre leachate was pumped out of the cave.

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SCALLOPS

The processing of the nitrate deposits of the sandstone rockcastles of eastern Kentucky is abbreviated. The nitrates from these shelter caves are typically potassium nitrate and do not require the ionic exchange step required for the calcium- and magnesium-rich nitrates of the carbonate solutional caves. Evidence of saltpetre processing in caves is important in establishing that the mining evidence is of saltpetre mining. Cave sediments have been excavated from caves worldwide for uses other than saltpetre extraction.

CONTRASTING SALTPETRE MINING WITH OTHER CAVE SEDIMENT EXTRACTION The cave sediments of many European caves are enriched not only in nitrates but also phosphate as a result of the bones of mega fauna, which used these caves during the Ice Ages of the Pleistocene. Locally, nitrate- and phosphate-enriched sediments have been extracted from European caves for fertilizing gardens. In China, cave sediments have historically been worked for fertilizer and for bones to be used in the apothecary trade. Marketed as “dragon bones,” these fossil remains have been processed for use in folk remedies and as aphrodisiacs. Bat guano has been utilized as fertilizer in numerous areas within the United States, but the extraction of other nitrate-rich cave sediments for garden use is also known from at least one U.S. locality. It is likely that European immigrants to the United States continued the time-honored traditional exploitation of enriched cave sediments as garden fertilizer at other southeastern U.S. sites. Evidence of the extraction of cave sediments without associated saltpetre processing evidence, written historic records of saltpetre mining, or local saltpetre mining lore may represent other uses of cave sediments, such as for garden fertilizer, chinking for a log home, ceramics, fossil or artifact pilferage, or other usage. In summary, saltpetre mining is a historic extractive industry tied to the development and usage of blackpowder-charged firearms. The archaic spelling of the mineral, saltpetre, is retained as a descriptor because, in most cases, this mineral has only rarely been encountered in saltpetre caves; rather, a suite of the deliquescent nitrates typically occurs as viscous solutions within cave sediments, which were mined and the nitrates extracted by leaching and chemically converted to the crystalline commodity, potassium nitrate (saltpeter), the major constituent of black powder.

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Bibliography DePaepe, D. (1985). Gunpowder from Mammoth Cave: The saga of saltpetre mining before and during the War of 1812. Hayes, KS: Cave Pearl Press. Duncan, M. S. (1997). Examining early nineteenth century saltpeter caves: An archaeological perspective. Journal of Cave and Karst Studies, 59(2), 91 94. Faust, B. (1964). Saltpetre caves and Virginia history. In H. H. Douglas (Ed.), Caves of Virginia (pp. 31 56). Falls Church, VA: Virginia Cave Survey. Hill, C. (Ed.), (1981). Saltpeter. National Speleological Society Bulletin, 43(4), 83 133. Hill, C., & Forti, P. (1997). Cave minerals of the world (2nd ed.). Huntsville, AL: National Speleological Society. Shaw, T. R. (1992). History of cave science. Sydney, Australia: Sydney Speleological Society. Smith, M. O. (1990). Saltpeter mining in East Tennessee. Maryville, TN: Byron’s Graphic Arts. Taylor, M. R. (1999). Dark life. New York: Scribner.

SCALLOPS Phillip J. Murphy University of Leeds, UK

INTRODUCTION Studies of the solutional sculpturing of cave walls can provide information on both the direction and discharge of water flow in a cave passage. Scallops are the most well-studied type of solutional sculpturing. Their asymmetry indicates the direction of groundwater flow and their wavelength are inversely proportional to the flow velocity. Laboratory and field investigations have enabled the calculation of mean flow velocity from scallop wavelength data and thus the calculation of discharge at the time of scallop formation.

SCALLOPS AND FLUTES Scallops are asymmetrical, cuspate, oyster-shellshaped dissolution depressions in cave walls. The term scallop was first proposed by Coleman (1949) to replace the term flute used prior to this. The term flute has been used for the elongate, nearly parallel crested forms seen in some cave passages. They are scallops of infinite width and are much rarer than true scallops. Vertical grooves seen in vadose shafts formed by water streaming down in thin sheets have also been called flutes.

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