What is the rent reserved on the demise of a marl pit and brick mine?

There is nothing, as it seems to me, in the objection that if the interest or arrears of interest are treated as the rent it is not a fixed or certain rent. It is always capable of being ascertained or reduced to a certainty, which is all that is necessary, and much more readily here than in Daniels v. Gracie, 6 Q.B. 144, where the rent reserved on a demise of a marl pit and brick mine was eight pence per yard for all the marl got out of the pit and one-eighth per thousand for all the bricks made out of the mine.