In the case of mines, oil and gas wells, other natural deposits, and timber, there shall be allowed as a deduction in computing taxable income a reasonable allowance for depletion and for depreciation of improvements, according to the peculiar conditions in each case; such reasonable allowance in all cases to be made under regulations prescribed by the Secretary. For purposes of this part, the term “mines” includes deposits of waste or residue, the extraction of ores or minerals from which is treated as mining under section 613(c). In any case in which it is ascertained as a result of operations or of development work that the recoverable units are greater or less than the prior estimate thereof, then such prior estimate (but not the basis for depletion) shall be revised and the allowance under this section for subsequent taxable years shall be based on such revised estimate.
In the case of property held in trust, the deduction under this section shall be apportioned between the income beneficiaries and the trustee in accordance with the pertinent provisions of the instrument creating the trust, or, in the absence of such provisions, on the basis of the trust income allocable to each.
For other rules applicable to depreciation of improvements, see section 167.