Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/173

nitrogen (and oxygen) up to 60 km. high, and above that the lighter gases.
Fig. 27.—Map of the continental blocks on Mercator’s projection. The zone of meteorological phenomena, which only reaches up to 11 km. (the troposphere), is too thin to be shown.

It has already been remarked that the material of these continental blocks is chiefly gneiss. But, as