STRIP PITS

In 1923, for the second year in succession, the production of bituminous coal from steam-shovel pits set a new record. Although the total output of soft coal fell short of that for 1920, the output of strip-mined coal showed an increase of 33 per cent (Table 44). The production of strip coal in Ohio and Pennsylvania declined slightly, but in Illinois, Indiana, and western Kentucky it showed a very large increase. The anthracite region continued to produce about the same quantity as in other recent years of normal output.

TABLE 44.—Coal recovered from steam-shovel strip pils, 1914-1923

The growing number of strip pits and the peculiar character of their operation make it advisable to present statistics of labor for such mines separate from the deep mines. Table 45 is a summary of the reports of all stripping operations that produced bituminous coal in 1923. As some companies develop their coal lands by stripping along the outcrops and by underground methods where the cover becomes thicker, it is not always possible to separate the particulars relating to stripping from the particulars relating to deep mining. Hence the table shows a considerable number of men employed underground, and the figures of days worked and the computed average output per man per day embrace their activities as well as those of the men engaged exclusively in stripping work on the surface.

The number of strip pits that produced coal in 1923 was 263. The number of shovels was 442, an average of somewhat less than 2 shovels to the pit. The quantity mined by stripping was 11,940,000 tons. Including coal recovered from underground operations the total output of the operations as a whole was 15,348,000 tons. The value of the strip coal proper can not be separated from the value of this coal won underground, but the total value of the entire product was $37,044,000, an average of $2.41 a ton. The lower costs of stripping are indicated by the fact that the average for all bituminous coal produced in 1923 was $2.68 a ton.

The total number employed by the operations embraced in the table was 12,654 men, of whom 9,332 worked on the surface.

The indicated production per man per day for the group of mines as a whole computed from the total quantity produced and the total number of men employed was 7.5 tons. Large as this figure seems in comparison with the 4.48 tons that represents the average for all mines in 1923, it is doubtless less than the actual daily production per man from the stripping operations alone could they be accurately segregated from the associated underground work. An approximation of the daily output per worker actually engaged in stripping may be had by dividing the tons mined by stripping by the product of the total number employed on the surface and the average days worked. This computation yields an average of 7.94 tons per man per day, a figure that agrees closely with the results of a special analysis of the production by methods of mining made in 1921 and published in the report on coal in 1922.18

This higher production per man per day is the clue to the rapid increase in the number and output of strip mines in recent years, High levels of wages, particularly in the union districts, have placed a premium upon economy in labor and favored the substitution of machine for hand methods.

The strip mines, however, suffer a disadvantage in being more subject to interruption by bad weather, whether violent storms in summer or heavy snows in winter; consequently, the average time worked by strip mines is less than the time of deep mines. The average for the 263 operations shown in Table 45 was 161 days; the average for all mines in the country 179 days. The location of stripping operations is governed by the occurrence of gently dipping beds of coal overlain by a few feet of cover in level country. The areas thus adapted to the method are the outcrops of the coal measures of the interior field and corresponding areas in the Pittsburgh and eastern Ohio fields. An interesting development is the rapid growth of stripping in the North Dakota lignite area, where ten pits produced in 1923 a total of 376,000 tons.

16 U. S. Geol, Survey Mineral Resources, 1922, pt. 2, p. 509, 1924.

TABLE 45.–Summary of stripping operations that produced bituminous coal in 1923—Continued