Where mining is done by shaft there is seldom any other way provided for the passage of workmen in and out than the way by the carriage. A small shaft for the admission of air is sometimes driven down to the highest part of the seam, and ladders are placed in the opening on which men may climb up and down, but these ladders are seldom used save in an emergency. It is made obligatory upon operators, by the act of 1885, to provide two openings to every seam of coal that is being worked; these openings to be at least sixty feet apart underground, and one hundred and fifty feet apart at the surface. The object of this rule is to provide a way of escape for workmen in case of accident to the main outlet. It is seldom necessary, however, in these days, to sink a separate shaft in order to comply with this provision of the law; the underground workings of the mines having such extensive connections that often not only two but many openings are accessible from each seam. As to the comparative cost of the different methods of entry, the drift is of course the cheapest. In this method the very first blow of the pick brings down a fragment of coal that may be sent to market and sold. For this reason the sinking of a slope is less expensive than tunneling or shafting, because the excavation is made in the coal. It may be said to cost from twenty-five to fifty dollars per linear yard to sink an ordinary double track slope, from fifty to seventy-five dollars per linear yard to drive a tunnel of average cross-section to accommodate two tracks, and from three hundred to five hundred dollars per linear yard to sink a shaft with four compartments. Of course circumstances, especially the character of strata, may greatly increase or lessen these limits of cost. Indeed, it has happened that a shaft in process of sinking, which had already cost many thousands of dollars, has been necessarily abandoned because an intractable bed of quicksand has been encountered. The experienced coal operator, knowing the advantages and disadvantages of each of these methods of entering a mine, and the adaptability of each to his particular coal bed, will find no difficulty in making a selection from them. Indeed, there may be, and usually is, practically, no choice. The selection of a site for the opening is ordinarily attended with but little more freedom of choice. The outcrop, if there be one, the topography of the surface, the outline of the coal seam, the accessibility of the spot, the location of the breaker, all govern in the selection of the site, and usually all point to the one most available spot. CHAPTER VIII. A PLAN OF A COAL MINE.