The writer of this article endeavored to show:(1) That the character of the aramaic emanations in the Yellowstone geyser-basins, and their function in hot-spring development, can be deduced from available evidence.(2) That these emanations all have the magma in the gaseous state.(3) That the water of these geyser-basins is largely (perhaps 85 to 90 per cent) of surface origin, and, because the supply is large, it descends to depths which a small supply could not attain without being wholly evaporated. At such depths the water dissolves and brings upward substances of low volatility, either magmatic sublimates or compounds formed at deep levels.(4) That the rock of these basins is an important factor in the development of the alkaline springs, yielding all the silica in both waters and deposits and at least an important part of the sodium in the former. This follows from the work of Fenner.