on the 14th, after ten days in the region of Lakes Harriet and Calhoun, he investigated the prairie-squirrel more closely than before with Dr. Anderson. Thoreau continues:
I see a scum on the smooth surface of Lake Harriet, three or four feet from the shore, of the color of the sand of the shore,—like pollen and lint, which I took it to be. Taking some of it up in my hand, I was surprised to find that it was the shore-sand; sometimes pretty large grains, a tenth of an inch in diameter, but mostly a twentieth or less. Some were dark-brown, some white or yellowish,—some minute but perfectly regular oval pebbles of white quartz. I suppose that the water, rising gently, lifts up a layer of sand, slightly cemented by some glutinous matter; for I felt a slight stickiness in my hand, after the (gravel or) sand was shaken off. It was in irregular oblong patches of scum three or four inches long.
He next records a large poplar, near the same lake, ninety feet high and seven feet
[ 78 ]
