Thoreau writes in his journal:
Got home at 1.30 P.M.
P. M.—To Walden.
Walden froze completely over last night. This is very sudden, for on the evening of the, 15th there was not a particle of ice in it . In just three days, then, it has been completely frozen over, and the ice is now from two and a half to three inches thick, a transparent green ice, through which I see the bottom where it is seven or eight feet deep. I detect its thickness by looking at the cracks, which are already very numerous . . .