DARWIN, Charles. Geological Observations on South America. Being the Third part of the Geology of the Voyage of the Beagle. London, 1846. 8o. Folding frontispiece map and 5 folding plates (some mild intermittent spotting). Original green pebbled cloth (recased, rear endpaper renewed, spine ends worn). FIRST EDITION. An apparently unrecorded variant as Freeman only describes copies in purple or blue cloth and with the map colored. This third part is the rarest of Darwin's three works on geology. Freeman 273 (variant). Norman 587 (similar binding).