I Have Seen...

...flocks [of passenger pigeons] streaming south in the autumn so large that they were flowing over from horizon to horizon in an almost contours stream all day long, at a rate of forty or fifty miles an hour, like a mighty river in the sky, widening, contracting, descending like falls and cataracts, and rising suddenly here and there in huge ragged masses like high-plashing spray.

- John Muir