40. Measure of damages.

By the rules of equity in claims of account, which are applicable in all courts1, the claimant is entitled to the market value of the minerals at the pit's mouth subject to certain allowances. The defendant may be allowed the cost of hewing and bringing to bank if he has acted inadvertently2, or under a belief of title in good faith3, or fairly and honestly4, or in cases of mere mistake in circumstances where there is no suggestion of fraud5, or where the mineral was worked under an expectation in good faith of a contract which the mineral owner