“The Glasgow, Paisley, Kilmarnock, and Ayr Railway Company,” who are represented by the Respondents, “hereby bind and oblige themselves to account for, and to pay the foresaid fixed rent, and the rent calculated on the quantity of minerals carried as aforesaid to the said Kilmarnock and Troon Railway Company;” “and it is hereby specially agreed to that the said rent shall be calculated as if the charge on minerals per ton were 1 ½ d ., although the carriage should be for a shorter distance than one mile.”