The process of but ing, as belbre described, is the same which has been long practised, and which is in common use at present. A new mode was invented and brought lorward under letters patent, some years ago, by Air. James Ryan, from Ireland. The principle is very ingenious, and it is this. The common boring rods are the same as before described ; but, in place of chissels, a forked cutting-tool is used, in the same way as Connelly described in the process of boring ; but, in place of the strata passed through being comminuted or ground to powder, a core or cylinder of the strata is formed; and as soon as the buying bit has advanced as deep as the shoulder of the fork, the rods are drawn up, and a pair of nippers substituted ; these seize the core, break it off, and bring it up. In this manner the boring proceeds through the strata to the required depth, and each piece of core brought tip, is laid in a horizontal direction, each piece regularly joining the preceding one at the line of fracture ; by this means, a true section of the strata bored through, with the coals found, is as distinctly seen as if 'a pit had been sunk through them. Besides which, the dip or declivity of the strata is also ascertain ed. It is said that the true line of dip can also be found during the process of putting down a single bore, but it is apprehended that the accuracy of the result cannot be depended on.
Mr. Ryan made every proper exertion to bring his ingenious mode of boring into practice ; a mode, the result of which was so satisfactory, leaving no ambi guity as to the strata passed through, and particularly as to the thickness and quality of coals, in ascertaining which so great mistakes have unfortunately taken place, because by the new plan the strata and coals in their na tural compact state are laid upon the surface of the ground. But highly satisfactory as this is, the plan has not succeeded, and is not yet known in common prac tice. Several eminent coal proprietors patronized Mr. Ryan, and gave his process a fair trial; the bores were not deep, but, so far as executed, they were satisfactory. The impression which the public has at present regard ing this mode of boring is, that it is very expensive, and not practicable in deep bores. It is, however, but too well known, how much mankind are attached to old plans, strongly prejudiced against new ones, and that it is no easy matter to change particular habits ; this may have operated against Mr. Ryan's invention, and have prevented success attending it. The bore-holes formed by the boring-bits are larger than those in common use, in order that the core may be about 3 or 4 inches diameter, and Mr. Ryan proposed by this plant() bore holes of more than one foot in diameter, to ventilate but it is supposed this did not succeed, or that the expense rendered it no saving. It is understood, however, that
by this process, with boring-bits and wimbles of large size, alluvial cover mixed with gravel and boulder stones has been passed through, where the old plans did not succeed ; and this kind of cover is the most difficult to bore through of any.
As boring for coal is always carried on in a line per pendicular to the plane of the horizon, and as coals and their accompanying strata, lie at every various angle of inclination to that plane, from nearly horizontal to the nerpendicular line, it results that the thickness of the strata, or of any coal bored through, if lying at a great angle with the horizon, will measure considerably more than what they absolutely are, because the true thick ness of any stratum or coal is only obtained by taking the measurement at right angles to the plane upon which each stratum or coal rests ; for example, in boring through the flat-lying coal, Plate CCCXC. Fig. 4. the difference betwixt the line passing through it, per pendicular to the horizon, and that which is at right angles to the plane on which it rests, is so trifling as need not be noticed ; but this difference betwixt the two perpendiculars, increases with the enlargement of the angle formed with the horizon so that in Fig. 5. the thickness of the coal, as ascertained by boring, is the distance a, b, whereas the absolute thickness of the coal is the distance b, c, that is, a line perpendicular to the plane on which the coal rests. In this example, the measurement of the coal by boring, is 16 feet, where as its absolute thickness, b, c, is exactly six feet, pro ducing an error of 10 feet. From these circumstances, it is not the practice to ascertain a coal-field composed of edge coals, by boring, because being nearly vertical, very few of the strata would be passed through, even with a deep bore ; therefore, when edge coals are not laid open to view in a ravine where the alluvial cover is removed, it is the practice, if the cover is not thick, to cut a trench through it at right angles to the line of bearing of the strata, and as edge coals lie generally at a short distance from each other, a trench of two hun dred yards in length will discover nearly that thick ness of the strata ; but if the cover is too thick for cut ting a trench to the rock head, the plan is, to sink a pit a few fathoms into the rock, from the bottom of which two mines are carried in a level direction, at right angles to the line of bearing, the one to the rise, the other to the dip of the strata. By this plan, the thickness and quality of the coals will be accurately ascertained. Fig. 6. skews the plan of proceeding with edge coals, a, a, are the edge coals, b the pit, c, c, the mines which in tersect the strata.