© 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. 'Among the grand and beautiful features of the globe are caverns, or natural hollows in the solid crust of the earth. Some of them are wide clefts in the rocks, others form a series of grottoes connected by pasages, while a third sort admit daylight at both ends. Some of these caverns are formed by the constant action of water on limestone or gypsum rocks; others are evidently due to volcanic agency.'