Thoreau writes in his journal:
P.M.—To Clamshell Hill, across river.
I see some cracks in a plowed field,—Depot Field corn-field,—maybe recent ones. I think since this last cold snap, else I had noticed them before. Those great cakes of ice which the last freshet floated up on to uplands now lie still further from the edge of the recent ice. You are surprised to see them lying with perpendicular edges a foot thick on bare, grassy upland where there is no other sign of water, sometimes wholly isolated by bare grass there. In the last freshet the South Branch was only broken up on the meadows for a few rods in width next the shores. Where the ice did not rise with the water, but, apparently being frozen to the dry bottom, was covered by the water,—there and apparently in shallow places here, then far from the shore, the ground ice was at length broken and rose up in cakes . . .