CHAPTER LXXXII.

LAND AND MINERALS.

BY PROFESSOR J. LOGAN LOBLEY, F.G.S.,

Professor of Physiography and Astronomy, City of London College; Lecturer on Geology, Crystal Palace School of Engineering; Vice-President of the City of London College of Science Society; Member of the General Committee of the British Association ; Member of the Geologists' Association; Hon. Member Hamp. F. C.; etc. Author of "The Study of Geology," "Geology for All," "Mount Vesuvius," Hampstead Hill," """The Inter-relations of the Field Naturalist's Knowledge,” “ The Cretaceous Rocks of England," "The Causes of Volcanic Action," ," "The Origin of Gold," etc.

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BESIDES coal and limestone, the presence of either of which at available depths is usually well known, not only to the proprietors but also to the inhabitants generally of the districts in which they occur, there are other minerals, both metallic and non-metallic, in British rocks that may give a high value to the overlying land.

Although Coal may be the basis of the wealth of this country, it will scarcely be denied that next to it, Ironthe iron of our machinery, our railways, and our great steamships-contributes most to that industrial activity, both in manufactures and commerce, which distinguishes the England and Scotland of to-day. The two ores that furnish our supplies of iron are Hæmatite and Clay Ironstone, the one a peroxide, and the other a carbonate of iron. Both of these are in bedded masses in the Carboniferous rocks of the British Islands, and the peroxide is so largely disseminated in some other rocks that

ore.

their most ferruginous beds are worked for this important In the Midlands Jurassic, and in the south of England Cretaceous, rocks are so worked; and in the last and the preceding century the chief seat of the iron trade of England was the Weald of Sussex, where ironstone nodules were reduced and metallic iron obtained by means of the charcoal of the wood of the oaks which there grew at that time in the greatest profusion. The ironstone nodules are still in the Wealden rocks in abundance, but the oaks have gone, and coal has not yet been worked in the south-east of England. With reduced charges for the conveyance of coal, it may be possible to work highly ferruginous beds with profit in localities where mining is now unknown. In many cases, such beds not forming hard rocks and being near the surface can be worked at small expense by open excavations or quarrying.

The Lead ores of the British Islands, though of less are of great importance, not only from the lead they yield, but also from the very considerable quantities of Silver some of them contain, for our chief lead ore is Galena, and much of it is argentiferous. This rich ore of lead, so well known from its conspicuous metallic aspect and splendid lustre, is, like coal and iron, an associate of Carboniferous rocks, though galena lodes are also found traversing other strata. It is extensively mined in the North of England, in Wales, and in the Isle of Man, and gives a large return for the capital expended. Though the silver in the galena is but a small proportion, yet from its high value it adds greatly to the profit of lead mining.

After silver it may perhaps not be out of place to mention Gold, since the precious metal has been obtained from several districts in these islands. Most persons

have been recently made aware of gold having been found in Wales, where it was evidently worked in Roman and perhaps in pre-Roman times. But the occurrence of gold in Wicklow, in Londonderry and other parts of Ireland, in Scotland, and in the west of England, is not so generally known, and few of the visitors to Edinburgh Castle are aware that the regalia there safeguarded and exhibited was made from Scotch gold obtained, in the days of James V. of the northern kingdom, from the beds of the streams in the Lead Hills district.

To the west of England Copper ore is, and has been for a long period, of great importance; for the mining industry of Cornwall, which has made that county famous throughout the world for its miners, has been largely dependent on its copper mines. The adjoining county of Devon also possesses very valuable cupriferous lodes. The ore of copper most abundant in English rocks is the sulphide, or sulphuret, of copper, commonly known by the name "copper pyrites," and the veins containing it are in Lower Devonian rocks, which are called in local language "killas." Associated with the copper pyrites, the Cornish and Devonian lodes contain considerable quantities of Blende, or "black jack," a sulphide of zinc, and a valuable ore of that metal, together with iron pyrites and other minerals. Ruby copper ore and melaconite, or black copper ore, both oxides of copper, as well as malachite, or green carbonate of copper, are also obtained from our English rocks, but not abundantly, and copper pyrites remains the chief ore of the metal in this country.

The Tin ore of Cornwall is much more famous than the ore of copper, and has been known and worked for a much longer period. In pre-Roman, or British times, tin-stone was exported to the then more civilized

This was

But

countries at the east of the Mediterranean. "stream tin," obtained from the beds of rivers and streams where the tin-stones had been accumulating, commingled with gravel, for vast periods of time. these stores having been so long and so largely drawn upon, the tin-stone now sought for is that of the lodes in the massive rocks. These stanniferous veins traverse the granitic rocks that are so prominent in the south-west of England. Tin-stone is the black oxide of tin, and often occurs in brilliant black crystals called "diamond tin," but sometimes it is brown or yellow, with a somewhat fibrous structure, and then called "wood tin." With it there is frequently associated much Schorl and Wolfram, a tungstate of iron. In Cornwall, too, near Gunnislake, an ore of Uranium has recently been found in considerable abundance.

There is another metallic mineral largely disseminated through English rocks that is of some economic value, though not used as a metallic ore. This is Iron Pyrites, a sulphide of iron, which, when it is obtained abundantly, as in the Isle of Sheppy, is used for the manufacture of sulphuric acid and sulphate of iron or green vitriol.

Of the non-metallic minerals obtained from British strata, Rock Salt has, after coal, the greatest economic value. In Cheshire, in Worcestershire, and in Yorkshire, beds of rock salt are very extensively worked with most profitable results. This deposit, the result of the evaporation of salt lakes in early Mesozoic times, occurs chiefly in the Triassic rocks, those usually called New Red Sandstone, and which wide-spreading and almost horizontal strata form the great midland plains of England. The beds of rock salt are so thick that the mineral is worked by large and lofty excavations underground that produce

caverns of great size, altogether unlike the low and narrow galleries of coal mines.

The Triassic rocks of England also contain very valuable beds of Alabaster and Gypsum. Both of these are sulphate of lime and much softer than marble, the carbonate of lime. This softness, together with its beauty and fineness of texture, renders alabaster admirably suited for carved ornamental objects, and for interior architectural adornment. Gypsum, which is less massive and more nodular, is of value for making plaster of Paris, and it is also used in the manufacture of glass and porcelain. Staffordshire, Derbyshire, and Cheshire have long been known as localities whence alabaster and gypsum are obtained, but they are by no means confined to these counties. The famous "Sub-Wealden Boring," near Battle in Sussex, undertaken under the auspices of the British Association, though it did not reach beds of coal as some expected, revealed the existence of a splendid and most valuable bed of fine white gypsum at no great distance from the surface, in strata determined to be of, in

geological language, Purbeck age. This is a striking illustration of the possibility of valuable minerals being under estates now known only as agricultural land.

Such another mineral is Barytes, or heavy spar, occurring also in Staffordshire and Cheshire, but found likewise in the south-east of England, in Surrey, where it occurs in fine crystals.

Fluor Spar, or Blue John, is a very beautiful mineral, that has been so long associated with Derbyshire that it is called Derbyshire Spar. It is a Fluoride of Calcium, and occurs in splendid cubical crystals, and also often massive, of very various colours, a rich blue or purple being perhaps the most common. Fluor Spar is obtained from the Carboniferous Limestone of Derby