“The nature of the compensation to be paid to the Mine Owner can not in my opinion be better expressed that it was by Lord Macnaghten in Bwllfa…namely that “so as far as money can compensate him he is to be placed in the position in which he would have been if he had been free to go on working…the hypothesis being that the Mine Owner is to receive by way of compensation for not working the minerals, what he would have made by working them…”