The Cordillera of the Andes in Tierra del Fuego is formed of crystalline schists, and culminates in the snow-capped peaks of Mount Darwin and Monte Sarmiento in the Cordillera Darwin, which contains glaciers of greater extent than those of Mont Blanc. The extent of the glaciers is considerable in this region, which, geographically, is more complex than was formerly supposed. Although, in the explored portion of the Fuegian chain, the volcanoes which have been mentioned from time to time have not been met with, there seem to have existed to the south, on the islands, many neo-volcanic rocks, some of which appear to be contemporaneous with the basaltic sheet that covers a part of eastern Patagonia.