'Natural bridges', 1849.
© Science Museum / Science & Society Picture Library
Colour engraving by Josiah Wood Whymper taken from 'Phenomena of Nature', published in London in 1849 for the Society for Promoting Christian Knowledge. 'The mountain chains of America are distinguished from those in Europe by perpendicular rents or crevices, which form very narrow vales of immense depth. These crevices can sometimes be crosed by natural bridges which unite two rocks of differing hardnes; the softer rock, being beneath the harder rock, having been eroded away.'