IRON. 



130 



rh:ch is at present wrought at Crossbasket. It varies in thick- 

 ness from ten to fourteen inches. Both it and the preceding 

 ore are reckoned of good average quality. This ore furnishes a 

 curious instance of the capricious and seemingly unaccountable 

 alterations that are liable to take place in every chemical manu- 

 facture, whose fundamental principles are little understood, and 

 in none, perhaps, does this happen more frequently than in 

 the smelting of iron. Although it forms the thickest of all the 

 Crossbasket strata, and therefore holds out powerful induce- 

 ments, in an economical point of view, to the iron smelter, it 

 was at one period regarded at the Clyde iron-works as an iron, 

 stone totally unfit for the manufacture of good iron ; and hav- 

 ing once received an unfavourable character, it was allowed to 

 remain umvorked for a long course of years. It is only of late 

 that its employment has been again resumed ; but, so far from 

 being held in low estimation, it is now considered to be little 

 inferior in quality to any of the Crossbasket ores, and is used 

 very extensively in the blast furnace. 



Immediately above this stratum there is situated a bed of 

 schist, containing- a regular stratification of very large nodules 

 of ironstone. Being extracted by the miner simultaneously 

 with the subjacent ore, they are used to a considerable extent 

 in the blast furnace, and are esteemed an ironstone of uncom- 

 monly fine quality. The black bituminous substance which occurs 

 occasionally in nodular ironstone, exists very generally distri- 

 buted throughout this stratification of balls. 



(e) A. specimen found in the neighbourhood of Clyde iron- 

 works, which are situated about four miles south-east from 

 Glasgow. Its mineralogical details are the following : Colour 

 pale, between brocoli-brown and clove-brown. Fracture rather 

 nne-grained, uneven. Not particularly hard, easily scratched 

 by the knife. Specific gravity 3.1482. The thickness of the 

 stratum is about two inches and a half. It is considered ut the 

 works to be an ore of a very inferior quality, and is seldom 

 smelted. 



Immediately above this ore there is situated a bed of schist, 

 which contains an immense number of petrifactions of different 

 kinds of bivalve shells : they consist of a very pure ironstone, 

 resembling in appearance the subjacent land. 



(/) Their forms are remarkably perfect, and they contain no 

 visible remains of the original shell. 



(/) An ore lying under the last-mentioned stratum, and in 

 close contact with it. Colour between yellowish-grey and hair- 

 brown. Fracture fine-grained, earthy, even. Rather hard ; 

 scratched with some difficulty by the knife. Specific gravity 

 3.2109. The stratum to which it belongs is situated above the 

 splint coal, with the intervention of only four inches of schist, 

 and both minerals are therefore worked out together with great 

 advantage to the smelter, It is the must valuable ore in all the 

 fields around Glasgow, except that called the black ironstone, 

 which is at present smelted at the Clyde iron-works. The 

 thickness of the stratum is between one and a half and two 

 inches. 



(g} This specimen was procured from Easterhonse, near the 

 line of the Monkland canal, and about six miles east from Glas- 

 gow. Colour clove-brown. Fracture fine-grained, rather 

 uneven. Somewhat tough and hard, but easily scratched by 

 the knife. Specific gravity 3.3109. 



This ore exists in precisely the same relative situation, with 

 regard to all the other accompanying minerals, as the two ores 

 from the Clyde iron-works, which have just been described ; and 

 wherever it makes its appearance, it seems to have been pro- 

 duced by the coalescence of these two strata. This compound 

 stratum has always a uniform texture and composition through- 

 out. Its average thickness is two and a half to three inches. 

 It is used pretty extensively in the blast furnace, and is esteemed 

 an ore of good average quality. 



(A) From the neighbourhood of Airdrie, about ten miles east 

 from Glasgow. Colour clove-brown, the intensity of the shade 

 varying considerably in streaks which are parallel to the direc- 

 tion of the stratum. When reduced to powder the colour is 

 brown. Fracture fine-grained, earthy, rather uneven. Toueh, 

 and difficultly pounded ; communicating a feeling of elasticity 

 under the pestle. Rather hard ; scratched by the knife. Ad- 

 heres slightly to the tongue, a property which did not appear 

 to be possessed in a sensible degree by any of the ores already 

 described. Specific gravity 3.0ft53. Numerous bivalve shells, of 

 a pale wood-browu colour, occur scattered through the mass of 

 this ore, and form a strong contrast with its darker shade. This 

 is one of the most valuable iron ores of Scotland, where it is 

 familiarly known under the name of black ironstone or Mushet't 

 black band. The latter appellation has been given from the cir- 

 cumstance that it was first smelted by Mr Mushet, to whom we 

 have already referred lu the metallurgist most distinguished for 

 his practical skill. 



It lies about fourteen fathoms below the fifth Glasgow coal- 

 bed, or splint ro;il, iind constitutes a layer about fourteen inches 

 in thickness. It is remarkable that it has hitherto been found 

 nowhere except in the neighbourhood of Airdrie ; although 

 several attempts have been made in other localities to reach it 

 by boring. At the Clyde iron- works, it is justly regarded as 

 the richest and most valuable ore which they at present possess. 



() From a stratum situated in the vicinity of Crossbasket. 

 Colour blueish-grey. Fracture, in the great, even; in the 

 juall, very fine-grained, earthy; rather hard. 



The foregoing table and remarks are taken from 

 Dr Colquhoun's paper, in Brewster's Edinburgh 

 Journal for 1827-8. 



5. Hydrous Oxide of Iron, and Brown Iron Ore. 

 The present is a species nearly parallel to the fore- 

 going, in the quantity of iron it affords to society. 



It is very rarely observed in distinct crystals, more 

 usually occurring in botryoidal and stalactical masses, 

 consisting of closely aggregated fibres, in which re- 

 spect it resembles the most common vareties of the 

 specular iron. The crystals are very sn.all, exter- 

 nally black and brilliant, and in the shape of right 

 rectangular prisms. The general character of the 

 species is as follows : lustre, adamantine : colour, 

 various shades of brown, of which yellowish-brown, 

 hair-brown, clove-brown, and blackish-brown are the 

 most common; streak, yellowish-brown ; brittle ; no 

 action on the magnet ; scratched by feldspar ; spe- 

 cific gravity, 3.922. Besides occurring in crystals 1 , 

 and in globular stalactitic and fruticose shapes, it is 

 found in masses whose composition is impalpable ; 

 sometimes also, the particles are so slightly coherent, 

 that the mass appears earthy and dull. It differs, 

 chemically, from the specular iron, in containing a 

 quantity of water, not merely interspersed through 

 its substance by simple absorption, but intimately 

 combined with it by chemical affinity. According to 

 D'Aubuisson, it consists of (in two analyses) 



Peroxide of iron, 82.00 . . 84.00 



Water, 14.00 . . 11.00 



Oxide of manganese, . . . . 2.00 .. 2.00 



Silica, 1.00 . . 2.00 



the proportion of peroxide of iron and water being 

 as 85.30 to 14.70. Before the blowpipe, it becomes 

 black and magnetic. It melts, with borax, into a 

 green or yellow glass, and is soluble in heated nitro- 

 muriatic acid. The division introduced among the 

 varieties of the present species, is somewhat similar 

 to that which has been given to red iron ore. Crys- 

 tallized hydrous oxide of iron embraces the small 

 black crystals, which sometimes occur in fibrous and 

 radiating bundles. Crystallized brown iron ore is 

 that variety which presents itself in the form of the 

 cube, rhomboid, or some modification of these forms, 

 and does not properly belong to this species, being 

 decomposed varieties of iron pyrites and spathic iron, 

 to which they are more correctly referred. The 

 fibrous brown iron ore, or brown hematite, contains 

 the fibrous varieties, in stalactitic, reniform, and other 

 imitative shapes. Compact brown iron ore compre- 

 hends those imitative shapes and massive varieties, in 

 which the composition or fibrous structure is no longer 

 observable ; while ochrey brown iron ore, or bog iron 

 ore, is applied to those which have an earthy texture 

 and are friable. As impure varieties of the species, 

 we must consider some of the clay iron ores, such as 

 the granular, the common, the pisiform, and the reni- 

 form clay iron ore. The granular variety is composed 

 of compact, roundish, or globular masses; the reni- 

 form one, of alternating coats, of different colour and 

 consistency, disposed in a reniform surface. In the 

 pisiform variety, we meet with a similar composition, 

 only in small globules, parallel to the surface of 

 which the lamella? are disposed. The compact pisi- 

 form clay iron ore, however, does not belong to the 

 present species, but it is decomposed iron pyrites, as 

 is demonstrated, not only by the crystalline forms 

 which it affects, but likewise from the nucleus of the 

 undecomposed pyrites, which the largest specimens 

 of it often embrace. The crystallized hydrous oxide 

 of iron is found, in limited quantities, in England, 

 France, and Siberia ; it either occurs in quartzose 

 geodes, in the form of mamillary masses, or is en- 

 closed in quartz crystals. The fibrous brown iron ore 

 is the most abundant and widely dispersed of all the 

 varieties of this species. It is commonly found in 

 large beds, in gneiss or mica-slate, and very frequently 

 in immediate connexion with granular limestone. It 

 is also found in Saxony and Thuringia, in beds and 

 veins, embraced, in some instances, in newer rocks. 

 It is uncommon in the northern countries of Europe ; 



