in Thoreau’s Journal:

Truly a hard day—hard Times these.  Not a mosquito left. Not an insect to hum. Crickets gone into winter quarters— Friends long since gone there—& you left to walk on frozen ground—with your hands in your pockets.  Ah but is not this a glorious time for your deep inward fires?— & will not your green hickory & white oak burn clean—in this frosty air?  

….All fields lie fallow —  Shall not your mind?  True the freezing ground is being prepared for immeasurable snows.— but there are brave thoughts within you that shall remain to rustle the winter through like white oak leaves upon your bough—or like scrub oaks that remind the traveller of a fire upon the hill sides—or evergreen thoughts cold even in mid summer by their nature shall contrast more fairly with the snow.