It is well known that under conditions prevailing at considerable distances below the earth’s surface silica is one of the more easily soluble of the substances entering into the composition of the earth’s crust. This is shown by the formation of secondary quartz veins, the solution and redeposition of quartz in both sedimentary and crystalline rocks, and, on a large scale, in the replacement of silica by other minerals, as in the case of the iron ores of the Lake Superior region. It is also well known that during the process of rockweathering under atmospheric conditions, by the breaking down of various silicates, much silica passes into solution. Merrill† has shown that in the passage of various crystalline rocks, as diabase and granite, from the fresh condition to that of soil, they suffer a larger absolute loss of silica than of any . . .