The laws which regulate the deposition of lead ore in veins; illustrated by an examination of geological structure of the mining districts of Alston Moor . ub-mitted to chemical investigation. The limestone strata are divided horizontally by thin beds ofargillaceous shale. Some of the layers are more susceptible ofdecomposition and change than others; and from this cir-cumstance they are termed flat posts. The Great Limestonecontains three posts of this character, respectively termed theHigh, Middle, and Low flat. In the Scar and Tyne bottom Lime-stones, posts more susceptible of decomposition
The laws which regulate the deposition of lead ore in veins; illustrated by an examination of geological structure of the mining districts of Alston Moor . ub-mitted to chemical investigation. The limestone strata are divided horizontally by thin beds ofargillaceous shale. Some of the layers are more susceptible ofdecomposition and change than others; and from this cir-cumstance they are termed flat posts. The Great Limestonecontains three posts of this character, respectively termed theHigh, Middle, and Low flat. In the Scar and Tyne bottom Lime-stones, posts more susceptible of decomposition than the rest arealso found to exist. When near to veins, the latter limestonehas undergone a greater degree of change and decomposition,throughout its entire thickness, than any other in Alston Moor. Near veins, large caverns are frequently met with in limestonestrata, more particularly in these flat posts. They are oftenbeautifully lined with crystals of various kinds of spar, but occa- 5« In 3 ^^^H f ^^/i ^IJJJiptUTff ^1 t .« N «: a >^ ^ i \ 5 * X o 1 2 5 § s V -^ zo ^< .< ^ ^ 1 II z1- UJ ?5 r IS(9 o CO s oto . ^J-W/ yhf^rf) ^2?^ut^. OF THE ROCKS. 135 sionally they present a jagged or corroded surface, with no liningof spars. A few years ago one was found between two portionsof Long Cleugh vein, in the High and Middle flat posts, thatcontained twenty cubic fathoms of open space, all lined withgalena. Black Jack, and carbonate of lime. Caverns of lesserdimensions than this are by no means uncommon; they are,however, seldom found larger. Where they occur in theNenthead mines, the limestone is a compact mass entirely freefrom joints or any fissures except veins. It is not an uncommoncircumstance to find a sandy residue left in the bottom of thesecaverns, which is sometimes slightly cemented into a porousmass, not unfrequently containing perfect crystals of galena. The caverns are, however, generally small, and had no mineralmatter been deposited in them, the limes
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1861
