466 R. C. WALLACE 



of similar type in salt flats, the fact of chemical erosion by sea- 

 water is emphasized by the study of the action of this essentially 

 similar brine. The chemical action of sea-water on igneous rocks 

 between high and low watermark must be much more considerable 

 than is generally believed. The disintegration attributed to 

 mechanical attrition is undoubtedly, in part, at least, chemical. 

 Sea-water under great pressure is apparently a solvent for the 

 volcanic debris which reaches the bottom of the deeper ocean; but 

 the solvent power is intensified by contact with the atmosphere, 

 even at ordinary pressures. Conditions are most suitable when 

 the three phases — solid, liquid, and gas — remain in intimate con- 

 tact for considerable periods of time. Such is the case where 

 shallow pools of water are imprisoned in the hollows of the rock 

 surfaces when the tide recedes; in these cases evidences of corro- 

 sion are very clear. 



It would be futile to attempt to compare in intensity the action 

 of sea-water on beach bowlders and that of rain-water impregnated 

 with humus acids from the soil. Data are not available in the 

 field. It must suffice, at this stage, to rank sea-water and acidified 

 rain-water side by side as two potent agents from the chemical, as 

 from the mechanical, standpoint, in the disintegration of rocks. 



