It is so rare to meet with a man out-doors who cherishes a worthy thought in his mind, which is independent of the labor of his hands.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“We were here locked through at noon by our old friend, the lover of the higher mathematics, who seemed glad to see us safe back again through so many locks; but we did not stop to consider any of his problems, though we could cheerfully have spent a whole autumn in this way another time, and never have asked what his religion was. It is so rare to meet with a man out-doors who cherishes a worthy thought in his mind, which is independent of the labor of his hands. Behind every man’s busy-ness there should be a level of undisturbed serenity and industry, as within the reef encircling a coral isle there is always an expanse of still water, where the depositions are going on which will finally raise it above the surface.” source