in Thoreau’s Journal:

I frequently see where oak leaves–absorbing the heat of the sun have sunk in to the ice & an inch in depth & afterward been blown out–leaving a perfect type of the leaf with its petiole & lobes sharply cut–with perfectly upright sides–so that I can easily tell the species of oak that made it. Sometimes these moulds have been evenly filled with snow–while the ice is dark–& you have the figure of the leaf in white.

in Thoreau’s Journal:

-5º.  A cold day;  Two or three inches of dry snow last night. 

Grows colder apace toward night.  Frost forms on windows.