Kingdom. 1
Class 1.—MINING AND MINERAL PRODUCTS.South Side—Areas S. 1 to S. 27.
169
or indirectly deriving a livelihood from some connectionwith lead-mining business. Allenlieads forms a centralposition in the midst of these mines, and the agent’shouse, shown on the section, is exactly 1,400 feet, abovethe level of the sea, and is the highest house of itsmagnitude in Great Britain,—nor are many of the cot-tages of shepherds, and other moorland habitations, ofgreater elevation.
The datum, or base line of the Allenheads section,is 700 feet above the level of the sea. The drawing,16J feet in length, is on a true scale of 100 feet to aninch ; by a true scale being meant, that the lengths andheights are projected to the same scale or proportion, sothat a true miniature profile of the country is given, aswell as a correct reduction of the relative size of thevarious rocks. The extent of country thus shown is notquite 4 miles, being 3 miles 1,220 yards.
The spectator is supposed to be looking to the north,and the section commences at a point about half a mileeastward from a place called Kilhope Head, which isconspicuously marked in all English maps, inasmuch asthe three counties of Northumberland, Durham , andCumberland all meet in one spot. At about three-quarters of a mile from the point of commencement, thesection represents the hill called Kilhope Law; it is onthe boundary line of the counties of Northumberland andDurham , and is the highest point of land in the last-named county, being 2,206 feet above the level of thesea. But out of the limits of this section, and about10 miles south-west from Kilhope Law, the same stratawhich are here delineated reach an altitude of 2,901 feetabove the sea, and this is the highest elevation attainedby the rocks which form the carboniferous or mountainlimestone of the north of England.
Such being the stratification of the central portion ofthe narrow part of the island, of which the coal-fields ofthe Tyne and Wear form the extremity on the east,bordering the German Ocean for some distance north andsouth of Newcastle , while a similar coal-field is found atthe western extremity near Whitehaven, it may beobserved, with reference to these coal-fields, that theylie over or upon the mountain limestone formation. Thecoal-beds so extensively worked in the Newcastle andDurham coal-mines, or collieries, gradually rise to thewest, and one by one crop out, or bassett, according to theundulations of the country. At length, at about 20 mileswest of the German Sea , the lowest of the coal-beds cropsout, and from beneath it gradually appear the lime-stone strata, which continue to rise nearly coincidentwith the general rise of the country until they reach thesummit of Cross Fell (2,901 feet); and this general andvery gradual inclination of the strata, a feature of thegreatest importance in practical mining, is clearly andaccurately delineated in this section.
In a thickness of about 2,000 feet of the alternatingbeds of sandstone, clay, and limestone, which form thestrata of the mining districts of Allendale, Alston, andWeardale, there is one single stratum of limestone calledthe “ great limestone,” the veins in which have pro-duced nearly, if not quite, as much ore as all the otherstrata put together. This stratum is delineated on thesection, and may be observed lying at a depth of about850 feet below the summit of Kilhope Law. Somewhatexceeding 2 miles eastward of this, at Allenheads, the topof the great limestone is 230 feet from the top of a shaftcalled Gin-hill Shaft. Its thickness, which is tolerablyuniform over several hundred square miles of country, isabout 60 feet, and it is from this stratum of limestonethat nearly all the specimens in this collection have beenobtained.
The dislocations of strata which constitute for themost part important mineral veins, are exhibited more indetail in the series of geological models which form a partof this collection; but some of the great features of dis-placement may be noticed on the section.
At about a quarter of a mile to the west of, or left-hand direction from, Kilhope Law, the great limestoneand all other associated beds are thrown down a depth ofabout 150 feet for a space of nearly 700 feet; and again,
at the distance of nearly a mile from Allenheads, a vastdislocation takes place, by which the great limestone, itwill be seen, is brought nearly to the surface, the amountof displacement being about 400 feet. It is in the greatlimestone that by far the most extensive portion of theworkings of Allenheads lead-mines are situated, and thegalleries drawn on the section convey a general idea ofthe position of the mines. In a great thickness of strataabove the great limestone only two beds of that rock arefound. One of these is called “little limestone;” it isfrom 10 to 12 feet thick, and is 75 feet above the top of thegreat limestone; the other is still more inconsiderable,being only 3 or 4 feet thick, and is 440 feet above thegreat limestone. It is remarkable with what exactnessthis thin bed is found near the summit of hills, the inter-vening spaces having apparently been removed by denu-dation, so as to form in one case a gap of 6^ miles, and inanother of If miles, in which the Tell Top limestone isentirely cut off.
But beneath the great limestone, as will be seen by thelines of blue colour, are several beds of the same descrip-tion of rock, viz., at distances respectively of 30,100,190,250, and 287 feet, and the thickness 2, 10, 15, 24, and 35feet. These are known by descriptive local names, andcomprise all that are of significance as regards lead-mining operations.
The Allenheads mines being situated for the most partat depths from the surface varying from 200 to 600 feet,are drained partly by ordinary water-wheels, some ofwhich are shown on the section, and partly by the newhydraulic engines invented by Mr. W. G. Armstrong , andfour of which are now in use for draining and othermining purposes at Allenheads mines.*
The isometricai, plan and section of Nentsberry,by the exhibitor, is intended to exemplify the mannerin which isometricai projection may be used in the de-lineation of mines and mining districts. In ordinaryplans and sections, only one plane, or set of parallelplanes can be truly represented, but by this method ofprojection three several planes may be combined in onedrawing, and lines crossing at right angles, as, for instance,north and south lines intersecting east and west lines,may be correctly projected, and vertical lines added onthe same projection.
The area represented by this drawing is about one-fourthof a square mile, each side being nearly half a mile inlength. It is situated on the River Nent, midway betweenthe source of that river at Nenthead and the market townof Alston. It includes some of the most interesting andprominent features of the strata and mines in that district,and amongst others the aqueduct called Nentfine Level,originally projected by the celebrated Smeaton , theengineer , who held the agency of these mines in 1775.
A copy of this section is deposited in the GovernmentOffice of Mining Records, and a further account of theseveral mining and other details is given in vol. ii. of“ The Transactions of the Natural History Society ofNorthumberland, Durham, and Newcastle-upon-Tyne .”
II. Models to illustrate Mineral Veins.— Plansand sections, although of great use, and indeed indispen-sable for all well-conducted mining operations, are yetincapable of conveying information relative to solid formsin so complete a manner as may be accomplished by theuse of models, which are, in fact, a reduced representationof the actual form of objects. The utility of models isfurther increased when they are made in separate portions,so as to admit of being dissected and put together again.By this means, not only the surface of the earth, but eventhe interior of mines may be correctly represented.
The models contained in the series now exhibited areexact duplicates of a series made for the Museum ofPractical Geology, and copies of which, on a smallerscale, are published. The details which accompany thepublished models may be had separately ; and the fol-lowing catalogue briefly indicates the principal pointsillustrated, as having a bearing upon the lead-miningdistricts:—