240 



partially decomposed, mixes with it as sand, and the 

 undecomposed quartz appears as gravel or sand, of 

 different degrees of fineness. As soon as the 

 smallest layer of earth is formed on the surface of a 

 rock, the seeds of lichens, mosses, and other imper- 

 fect vegetable bodies which are constantly floating 

 in the atmosphere, and which have made it their 

 resting place, begin to vegetate ; their death, decom- 

 position, and decay, afford a certain quantity of 

 organisable matter, which mixes with the earthy ma- 

 terials of the rock ; in this improved soil, more per- 

 fect plants are capable of subsistence. These, in 

 their turn, absorb nourishment from water and the 

 atmosphere, and, after perishing, afford new materials 

 to those already provided ; the decomposition of the 

 rock still continues, and at length, by such slow and 

 gradual processes, a soil is formed in which even 

 forest-trees can fix their roots, and which is fitted to 

 reward the labours of the cultivator." 



We cannot better illustrate the general character 

 of our mineral treasures than by briefly referring to 

 that universally diffused one iron. The immense 

 supplies for the arts of life are usually drawn from 

 the oxides. It is so abundant that there are few 

 fossils free from it, and many mineral waters contain 

 it. When we examine any chasm in the earth's sur- 

 face, it will generally be found tinged with a reddish 

 hue, and the intensity of the colour will generally 

 furnish some indication of the amount of ferruginous 

 matter that it contains. But a better and equally 

 simple test may be found in the use of a little of the 

 infusion obtained from bruised gall nuts in water, 

 which on being blended with the suspected body will 

 become of a dark colour. This mode of ascertaining 

 the presence of iron is exceedingly valuable as, on 

 account of the universality of this mineral, there are 

 many sites entirely valueless as domestic residences 

 from the quantity of iron with which the water is im- 

 pregnated. But we are not to suppose from this that 

 pure or native iron can be raised from the earth in 

 every region, as the cases in which it really occurs 

 are very rare. Where it is so found there can be little 

 doubt that it is generally of meteoric origin. Such 

 for example is the mass weighing about 1600 pounds 

 found by Professor Pallas in Siberia, and a mass 

 weighing fifteen tons discovered by Rubin de Celis 

 in Peru. 



There are several varieties of mineralised iron which 

 generally consist of the metal combined with oxygen. 

 Indeed the native oxides constitute a very extensive 

 and important class of metallic ores. They vary in 

 colour, depending upon mere texture in some cases ; 

 in others, upon the degree of oxidisement. Some 

 varieties are magnetic, and those which contain least 

 oxygen have the greatest magnetic power. The 

 haematite, or red iron-stone, is of a very peculiar cha- 

 racter. It occurs in globular and stalactitic masses, 

 and it may be proper to observe tnat most of our iron 

 plate and wire is made from it. But clay-iron-stone 

 is the mineral which produces the greatest quantities 

 of cast and bar iron. This in a great measure arises 

 from the proximity of coals with which it is usually 

 accompanied. 



When we look at either of these minerals, it must 

 be sufficiently obvious that they bear but little resem- 

 blance to the bright and shining body to which they 

 are afterwards reduced. The essential part of the pro- 

 cess by which this is effected consists in decomposing 

 them by the action of charcoal or coke at high tempe- 



ratures. Thus ihe argillaceous iron of Wales, Shrop- 

 shire, &c., is first roasted, and then smelted with 

 limestone and coke ; the use of the former being to 

 form a fusible compound \\ith the clay of the mineral 

 by which the latter is enabled to act upon the oxide, 

 and to reduce it to the metallic state. 



Our space will not admit anything like a detailed 

 history of the science of mineralogy, or of the various 

 systems of classification that have been pursued ; 

 and, for a view of the mineral bodies themselves, we 

 must refer the reader to their alphabetical order in 

 the present work. It may, however, be proper to 

 state that as a science it is little more than half a 

 century old. Previous to that time fine collections- 

 of minerals existed, but more advantage may now be 

 derived from studying the beautifully arranged cases 

 of specimens in the British Museum for a single 

 morning, than could have been derived from a life- 

 time according to the old and inaccurate mode of 

 classification. In the beginning of the last century 

 the descriptive language of mineralogy was vague 

 and ambiguous, each author using that which seemed 

 to him best to answer his present purpose. Now, 

 however, a slight acquaintance with chemistry and 

 the mathematical sciences enables the mineralogist 

 to as accurately discriminate his specimens, and com- 

 municate his knowledge to others, as in the classifi- 

 cation of a library. 



The celebrated Berzelius has attempted to esta- 

 blish a pure scientific system of mineralogy, by the 

 application of the electro-chemical theory and the 

 doctrine of chemical proportions. The views which 

 he disclosed are novel and highly important. He 

 defines mineralogy to be the science which treats of 

 thfl elementary combinations of inorganic substances 

 found in or upon the earth, and of the various forms 

 and different foreign admixtures under which these 

 bodies make their appearance. The object of Berze- 

 lius is to shew that the influence of the electro-che- 

 mical theory extends as much to mineralogy as to 

 chemistry ; and also that the doctrine of definite 

 chemical proportions is equally applicable, and will 

 give the same degree of mathematical certainty to 

 the arrangements of a mineralogical system which it 

 has already given to chemistry. " From the electro- 

 chemical theory we have," says he, " been taught to 

 seek in every compound body for ingredients of oppo- 

 site electro-chemical properties, and we have learned 

 from it that the combinations cohere with a force which 

 is in proportion to the degree of opposition in the 

 electro-chemical nature of the ingredients. Hence it 

 follows, that in every compound body there are one 

 or more electro-positive, and one or more electro- 

 negative ingredients. By electro-positive ingredients 

 he designates such as have inflammable bodies, or 

 salts for bases ; and, by electro-negative, the oxygen 

 and oxides which go to the negative pole ot the 

 voltaic battery. In other words every substance 

 called a basis, in chemical combination, must have 

 another which acts the part of an acid, though the 

 latter, when uncombined, may not be distinguished 

 by an acid flavour, or the property of changing vege- 

 table blues to red. The body which, in one case is 

 electro-negative, may, in another case, be electro- 

 positive, and may be united to a stronger electro-ne- 

 gative, that is, it may be the basis to a stronger acid. 



Berzelius divides simple bodies into three classes; 

 Oxygen simple combustibles not metallic, or metalloid, 

 and metals. A general notion of their arrangement 



