Coal Resource Classification System of the U.S. Geological Survey
By Gordon H. Wood, Jr., Thomas M. Kehn, M. Devereux Carter, and William C. Culbertson
GEOLOGICAL SURVEY CIRCULAR 891
1
Table 4. - Areas of reliability from figure 13 listed by overburden and coal thickness categories, and by countries
[Tonnage estimated for each area could be determined (1) by planimetering each area for acreage, and (2) by multiplying acreage by proper weight of coal per acre-inch by the average thickness of coal in the area. Average thickness of coal would be obtained by isopaching coal thickness as shown on figure 13]
| Geologic Assurance Category | Coal thickness | |
| 14 to 28 inches | 28 to 42 inches | |
| 0 to 500 feet overburden: | ||
| Measured | A, B, C | None |
| Indicated | D, E, F | Do. |
| Inferred | G, H, I, J, K | Do. |
| 500 to 1,000 feet overburden: | ||
| Indicated | L, M, N | None |
| Inferred | O, P | Do. |
| 1,000 to 2,000 feet overburden: | ||
| Inferred | Q, R | None |
| 2,000 to 3,000 feet overburden | ||
| Inferred | S, T | None |
| Hypothetical | U | Do. |
| Political division | ||
| Holmes County | Dead Bull County | |
| A, F, G, H, N | B, C, D, E, I, J, | |
| O, R, S, U | K, L, M, P, Q, T | |
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