Dear Sir

Pray excuse me for troubling you with a few lines to explain how I fell into the horrid blunder about the amount of ejected earth per acre.¹ I find in my notes a calculation on the assumption that the worms worked during 45 days & a second calculation on their having worked for only 40 days, & I concluded this latter period was probably more correct as the drought had lasted 2 or 3 weeks than 45 days, but forgot to alter the number of days.

Once again thanking you & begging you to excuse me for troubling you, I remain, Dear Sir | Yours faithfully | Ch. Darwin

P.S. | One of my sons, who is trustworthy, finds the relation between the weight for square yard & for acre correct, as I have given it.—²