From Amy Ruck to Horace Darwin   [1 February 1872]¹

Will you tell M^r. Darwin that in the case in which the furrows run down the hill & are 4ⁱⁿ at the top & 1ⁱⁿ at the bottom—the slope is 15^o and faces North East. The furrows are about 7 f^t apart & on the level ground above are 4ⁱⁿ 3$\frac{1}{2}$ⁱⁿ deep, although it is difficult to measure these on account of the mole hills—40 paces long.

On another slope of 15^o facing S. West the furrows were scarcely perceptible but on level ground at the bottom the same furrows were 3$\frac{1}{4}$ 2$\frac{1}{2}$ⁱⁿ deep. The length of the slope was 80 paces— On another short slope of 10^o the furrows at the top were 3$\frac{1}{2}$ at the bottom 1$\frac{1}{4}$ 1$\frac{1}{2}$ⁱⁿ deep.²