31 I N E. 



325 



M!r of plying the perpendicular distance by what i termed 

 lu-i. the n distance betwixt two coals is u-n 



s "" ~f~~* fathoms, and the dip 1 ir. 5, then 10x5 gives 50 fa- 

 thoms fur the distance in the horizontal section at the 

 crop, or if the horizontal distance and dip are known, 

 then the lior/ontal distance divided by the dip gives 

 the perpendicular distance betwixt the two coals, viz. 

 50 divided by 5 give* ten fathoms perpendicular dis- 

 tance as above. 



Having thus endeavoured to shew, that when coal- 

 fields are not viewed upon a limited, but an extended 

 scale, that they form either circular, or more generally, 

 long elliptical basons, or portions of this figure, though 

 sometimes in an inverted position, it must trom this cir- 

 cumstance appear evident, tint every coal and iu ac- 

 companying strata will crop out and meet th alluvial 

 cover, excepting when they are cut off and prevented 

 from doing so by slip*, or where they form portions of 

 an inverted b -son, or take u counter dip, as may be 

 een by inspecting the preceding figures relative to the 

 ahape of coal-fields. In the foregoing examples, the 

 coals and accompanying strata we considered as keep- 

 ing nearly the same distance from one another in each 

 coal-field, and that they keep nearly the same paral- 

 lelism a* to the angle of dip and rise, with the 

 quality of the coal unaltered in the several coal-fields 

 produced by the lips and dislocations of the strata. 

 In many instances we find this to be the case ; but 

 many changes are found to be produced, such as 

 alterations in the angle of dip and rise, of the strata 

 before coming to slips or dislocation*, a general 

 change in the angle of dip and rise in the coal-field 

 formed beyond them, some of the coals varying in thick- 

 one in the different coal-fields separated by these 

 lips, and sometimes the thickness of the strata betwixt 

 two bed* of coal is doubled ; at other times the distance 

 betwixt them is rendered so little in some instances, as 

 to be no longer visible ; by which means, two seams of 

 coal which were wrought s distinct beds of coal, are join- 

 ed together, form one bed of coal, and wrought a* such. 

 Instances are also found of beds of coal composing a 

 coal-field on one tide of a slip disappearing on the other 

 side ; but this doe* not take place with the chief or 

 main beds of coal. Differences, in point of quality, are 

 occasionally found in the coals divided by slips and dis- 

 location!), though it is clearly evident tliat it is the same 

 formation of coal-field on each side. 



Eittnt of Although coal-fields are of the form as before describ- 

 ciMl-feldj. ed, it must be remembered that the extent of a single 

 coal-field, in the line of bearing, is found to be several 

 miles in length, suppose six miles ; that is, they art 

 sometimes found of this extent, without any great dis- 

 locations as to nave the effect of forming new coal. 

 fields ; and they are found in the line of dip and rise to 

 extend above two miles. Other coal-fields are very 

 mall, not extending to half a mile in the line of bear- 

 ing ; yet, from the extent of the coal-basons, we must 

 remark, that, in considering the shape of a small por- 

 tion of a coal-field, and the operations connected with 

 the working of it, the idea of the bason-shape is aban- 

 doned, and the coal-field and beds of coal are considered 

 as a regular lying inclined plane. This, upon a limited 

 scale, is nol far from the truth, considering the great ex- 

 tent of the basons ; but this idea will evidently be found 

 very erroneous the instant a coal-field is viewed upon 

 an extended scale, and extensive operations pursued in 



fcawhing The next point to be described, is the methods com- 

 monly pursued by mineralogists and miner* in searching 

 for coal*, premuuig, however, that a clear idea ha* 



been formed of the facts before stated, as to the general Mi* u f 

 natural phenomena connected with coal-fields. In mak- ,_^f' l '_ l , 

 ing a survey in search of coals, there are two distinct "" """Y"" 

 points of survey to be attended to. 



Itt, The searching for coal in a district of country 

 where no coals are known to exist. 



2rf, The searching for coal in a district of country 

 where the coal formation is known to be, or where coals 

 are working at no great distance from it. 



In searching for coals in a district of country where Searching 

 no coals are known to exist, the first point for considera- for coali in 

 lion is the general aspect and outline of the country un- ""strict 

 der survey. Although, from taking this general view, "J^*,, 

 we cannot determine whether it contains coal-fields or knom . n , 

 not. yet, if the country is composed of hills or moun- ei j s ,. 

 tains, with steep acclivities precipitous rocks, and sharp, 

 and rugged summit*, with narrow valleys betwixt the 

 mountains, we have no reason to expect that strata will 

 be found there containing coal ; and excepting this very 

 obvious and plain feature, as to aspect, we do not know 

 any other upon which we can conclude, with any de- 

 gree of certainty, whether coals will be found in a dis- 

 trict of country or not. 



It must, however, be remarked, that, in the second 

 coal formation of Werner, as noticed in the geological 

 view of the situation of coal-fields, that though the great 

 bed* or masses of greenstone overlying a coal-field do not 

 rise into what may be denominated mountains, they form, 

 in this singular variety of the coal-field, hills several hun- 

 dred feet above the level of the sea, with rugged preci- 

 pices, rudely columnar, in some instances nearly 20O feet 

 nigh, under which coal is not only found occasionally, 

 but in amazing thickness, though not of great extent. 

 Thi* is therefore a rugged aspect, firmed l>y n peculiar 

 kind of rock, under which coal is occasionally found. 



This, we apprehend, is all that can be said regarding 

 the general aspect of a country, as to whether it con- 

 tains the coal formation or not ; for when it is known 

 that coals are found not only at great depths under the 

 sea, but at very considerable heights above it, even so 

 high as to form with their concomitant strata consider- 

 ble hills, we may, from these circumstances, infer, that 

 coals are found under every variation of surface, such a* 

 the ocean's sandy shores, the recent and old alluvial co- 

 ven, and also under every kind of varied 'nil and dale. 

 But we must observe, that there are also vast district* 

 of country with all these varieties of surface, and exact- 

 ly similar in aspect, under which no coal* are to be 

 found. This shews how limited our conclusions are 

 from the aspect of a country, whether it contains th 

 coal formation or not. 



It thus appears that no conclusions can be drawn, 

 with any degree of certainty, from the aspect of the 

 country, a* to whether coal* are to be found in it or not. 

 But mineralogists, who have surveyed many countries, 

 and who have had an opportunity of examining the pe- 

 culiar character, outline, and forms of mountain* and 

 hills, arising from the nature or kind of rocks constitut- 

 ing their mass, conclude, from the aspect in general, 

 very correctly, of what rock* they are formed ; but this 

 discrimination is not applicable to coal-fields, as the 

 rocks which compote the variou* beds, alternating with 

 the coal, are, in general, much softer than the moun- 

 tain rocks, and form few or no precipices. Where the 

 coal formation forms a group of hills, they have the ap- 

 pearance of some of the transition class, with the ex- 

 ception of being -otter in their contour and outline*; 

 but this does not afford a distinction of character suffi- 

 ciently preci-e, as the long running ridges of hills of 

 moderate elevation, forming the hiU and dale country 



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