Charles Darwin,
Coral Reefs; Volcanic Islands; South American Geology…
“ In three places [X, Y, Z] masses of andesite are exposed: at [Y] , this rock contained some quartz, but the greater part consisted of andesitic porphyry, with only a few well-developed crystals of albite, and forming a great white mass, having the external aspect of granite, capped by much dark unstratified porphyry. In many parts of the mountains, there are dikes of a green colour, and other white ones, which latter probably spring from underlying masses of andesite. ”
