MINING 295 



places, and particularly at "Whitby and Guisborough in Yorkshire, for the manufac- 

 ture of alum and copperas. 



Within the last few years, most important beds of stratified iron ore have been 

 worked in the marlstone, or middle lias in Cleveland, in the north of Yorkshire. 



Strata of iron ore also occur in the overlying oolitic limestones, in Yorkshire, Nor- 

 thamptonshire, and other parts of England. The same formations have in France 

 long been noted for the supply of large quantities of iron ore. 



The Lower Greensand beneath the chalk formation is often so strongly imbued with 

 iron as to have led in former times to extensive mining operations and iron smelting in 

 the south-eastern part of England. Since the general introduction of railways, attempts 

 have again been made to utilise those iron deposits. 



The lowest beds of the chalk contain iron pyrites, which has become the object of 

 an important exploration at Vissans, on the southern coast of the Pas-de-Calais, where 

 it is converted into sulphate of iron. The waves turn the nodules out of their bed, 

 and roll them on the shore, where they are picked up. 



If the chalk be poor in useful minerals, this is not the case with the tertiary 

 formation above it; for it contains important mines. In it are explored numerous 

 beds of lignite (wood-coal), and from some of these lignite deposits, also, yellow amber 

 is extracted. The iron mines of the north-east of Ireland, previously noticed, are in 

 deposits of basalt of miocene age. 



The other tertiary formations present merely a few mines of sulphur, of iron and 

 bitumen ; but it must here again be remarked, that many of the secondary, and even of 

 tlie tertiary strata have in certain countries been subjected to metamorphic action, of 

 such a nature as to have led to their being classed with the older rocks ; and thus 

 some of the metalliferous formations of the east of Europe and of South America, 

 although still somewhat obscure, ought without doubt in strictness to be classified 

 with these more recent deposits. 



Several of the secondary or tertiary strata contain deposits of sulphur, which are 

 mined in various coiintries. 



The formations of a decidedly volcanic origin afford but few mining materials, if 

 we except sulphur, alum, and opals. 



MINES OF THE ALLUVIAL STRATA. 



This formation contains very important mines, since from it are extracted all the 

 diamonds, and almost all the precious stones, the platinum, and the greatest part of the 

 gold, with a considerable portion of the tin. The diamond mines are confined nearly 

 to Brazil, and to the kingdoms of Golconda and Visapour in the East Indies. The 

 South-African diamonds are found partly in river-beds, and partly in ' dry diggings.' 

 See DIAMOND. 



The tin-stream works of Cornwall, Bohemia, and the East Indies, and the gold- 

 washings, placers, or ' diggings ' of Siberia, Borneo, California, and Australia, 

 belong to beds of alluvium or drift, irregularly deposited over the older formations. 

 See GOLD ; TIN. 



IMEIKrilTG. As the operations of mining vary with the conditions of the rock- 

 formations, in which the minerals sought for by the miner occur, it is necessary to 

 give a brief description of the more especially marked distinctions which are seen in 

 our geological formations. 



Geologists divide rocks into stratified and unstratified. Those mineral systems, 

 which consist of parallel, or nearly parallel planes, whose length and breadth greatly 

 exceed their thickness, are called stratified rocks ; while to those which occur in thick 

 blocks, and which do not exhibit those parallel planes, the term of unstratified rocks 

 is applied. These formations have been divided into two other classes, namely, the 

 primary and the secondary. The advances of geological science, however, and more 

 accurate information, have materially modified the views which gave rise to those 

 divisions ; and when men have learned to look on great natural phenomena without 

 the interposition of the medium of some favourite theory, there is but little doubt 

 the interpretation will be somewhat different from even that which is now received. 



A certain set of rocks may be classed as of truly igneous origin. These are the 

 traps, basalt, and the like. These have often been termed primary rocks. Yet we 

 have rocks of this class, not merely forcing their way through the superincumbent 

 and more recent rocks, but actually overflowing them ; they in many cases, therefore, 

 are much more recent than the secondary rocks. Granite has commonly been classed 

 as a truly igneous rock ; but facts have lately been developed which show, at all 

 events, the combined action of water. See GRANITE. 



Granite is' usually classed with the unstratified rocks ; but the section of any 



