326 



MINE. 



Mines of which contains coals, present, like other ridges, a line of 

 horizon nearly level, with few or no indentations, and 

 V-Trchhv ' no ^^P 1 precipices, excepting when greenstone or ba- 

 Corraab. sa ' t occurs, either overlying the strata, or forming a 

 dike in the coal-field, and rising above the other softer 

 strata. This situation of the greenstone is altogether 

 different from that of the greenstone in the second coal 

 formation of Werner. The long ridges containing coal, 

 and forming what is termed a tame horizon, are very 

 similar to the hills composed of chalk. It is to be re- 

 marked, that the line of bearing of the hills and dales 

 is somewhat in the direction of the large rivers or main 

 trunks of rivers, which drain the district of water. 



Since so very little can be depended upon, as to the 

 conclusions to be drawn from the aspect of a country 

 regarding coals being found in it, the next step is to ex- 

 amine the surface, or alluvial cover, which, in most cases, 

 hides the strata underneath from view. Were it not for 

 this cover, the searching for coals and other minerals 

 would be a very plain and simple process ; and, as this 

 cover is frequently many fathoms in thickness, and 

 sometimes of very heterogeneous composition, the pit- 

 ting or boring through it is often attended with consi- 

 derable difficulty. 



If the district under survey for coal is composed of 

 the bleak and sandy shores upon the margin of the 

 ocean, or of the recent alluvial land at the mouth, and 

 along the course of large rivers, whose waters move 

 with a slow current, it very seldom happens that any 

 symptoms of the kind of strata underneath can be dis- 

 covered, even although these covers be examined to a 

 considerable depth, as it is not common to find any 

 fragments of the adjoining rocks mixed with them. We 

 have seen these covers passed through to the depth of 

 ninety feet, without finding even the smallest fragments 

 of stone, nothing being found larger than grains of sand. 

 As these sandy and earthy deposites, which cover the 

 rocks upon the margin of the ocean, and by the sides of 

 slow running rivers, are very flat, and rise inland with 

 an imperceptible angle of elevation, it seldom happens 

 that any discovery of the rocks can be made, either in 

 the beds or sides of the rivers and brooks which flow 

 through them; therefore, in all such cases, recourse 

 must be had to pitting and boring, in order to ascertain 

 the kind of rocks underneath, and whether they belong 

 to the coal formation or not. The plans commonly 

 adopted for passing through the alluvial covers will be 

 afterwards described, when treating of boring. 



As we proceed inland, the recent alluvial cover be- 

 comes thinner, and disappears at its line of junction with 

 the old alluvial cover, which line is, in most cases, very 

 distinct. This kind of cover forms frequently a hill 

 and dale country, considerably elevated above the level 

 of the sea. The rivers and brooks which intersect it 

 often expose the rocks to view, so that it can be deter- 

 mined, from inspection, to what class they belong. 

 Therefore, in such a country, the first step to be taken 

 in the survey in search of coal, is to investigate the 

 beds and sides of every river and brook, noting the 

 kinds of rock which appear, and also their dip and line 

 of bearing. Every piece of broken ground and quarry 

 must be examined in the same manner. 



Springs of water require also to be examined ; and 

 although those which have an ochrey deposit, are not to 

 be supposed as affording unequivocal symptoms of coal, 

 yet they are sometimes indicative of coal, or of ironstone 

 accompanying coal. At the same time, it must be re- 

 marked, that these ochrey deposites are found in waters 

 which drain through common clay; and often very 

 abundant from peat earth. 



If, after heavy rains, which cause springs to flow co- 

 piously, small bits and grains of coal are found thrown 

 out by the water, we have reason to conclude that coal 

 is to be found at no great distance ; and the searching 

 for it must be proceeded in accordingly. 



If, in the sides of rivers, brooks, or broken ground, a 

 black sooty appearance is seen, this is frequently found 

 to be the crop or outburst of a coal, and ought to be 

 followed in the line of dip, by throwing an open trench. 

 If it is the crop of a coal, the sooty appearance will be- 

 come more compact as the operation proceeds to the dip. 

 Small shining angular pieces of coal will be found mix- 

 ed with it; and at last coal, apparently solid, but still 

 very friable, will succeed, resting upon the pavement 

 of the coal. The trial must proceed, until the roof is 

 found firm, regular, and parallel with the pavement. 

 It frequently happens that all the natural cracks and 

 fissures of the coal near the crop are filled with clay, 

 which gives the coal a very unpromising appearance ; 

 yet this disappears after proceeding a few fathoms more 

 to the dip. When a coal is found regular as a stratum 

 betwixt the pavement and roof, we conclude that the 

 full thickness of that particular bed of coal is found, 

 providing we see no appearance of any of the disloca- 

 tions or troubles before described, which must be kept 

 in view when drawing conclusions from the appearance 

 of coals, when thus found. After a bed of coal is found 

 regularly formed, as before described, if its absolute 

 situation and thickness farther a dipping is required to 

 be known; or, if the strata lying either above or below 

 it are to be investigated in search of other beds of coal, 

 these points must be ascertained by pitting and boring. 



In the face of steep banks of earth, even when the 

 ground is not broken, the crops of coals are frequently 

 observed by a black colour given to the soil ; which 

 appearance is also observed in lands which have been 

 recently ploughed. When this appearance is seen in 

 the face of a steep bank, the search for a bed of a coal 

 should proceed to the rise, or a little higher up the bank 

 than where the black colour appears. But when this 

 appearance is found in flat ground, a trench must be 

 cut at right angles across it, so as to ascertain the line 

 of dip; and, when this is found, the investigation will 

 go forward in the line of dip, as before directed 



If, by ths sides of rivers or brooks, pieces of coal are 

 found much rounded in the angles, it is to be inferred 

 that the bed of coal from which the fragments have 

 been detached is at a considerable distance from the spot 

 where they are found ; but if the angles are sharp, it 

 may be concluded that the bed of coal from which they 

 come is at no great distance. 



In digging through the old alluvial cover which rests 

 upon a coal-field, numerous fragments of coal, and of 

 all the accompanying coal strata are found, as well as 

 small rounded gravel of the mountain rocks, and large 

 boulder stones. It is remarkable that the fragments of 

 coal, and of the coal strata, are, in general, not worn 

 by attrition, but are sharp and angular ; which show, 

 that the formation of this old alluvial cover was by 

 water in a very different state from that by which the 

 recent alluvial cover has been formed, and is daily form- 

 ing. Yet though these appearances give evidence that 

 the district contains the coal formation, they do not 

 point out in what direction the crops of the coals from 

 which they have been detached are to be found. It is 

 proper to remark, in this place, that though unequivocal 

 symptoms of coal are found, and that it may be inferred 

 that we are within a coal formation district, yet we can 

 conclude nothing satisfactory, as to the thickness of the 

 beds of coal, until proper trials are made. 



