224 M. R. CAMPBELL — EROSION AT BASELEVEL. 



We can very easily account for that portion of the material in question 

 which is usually considered soluble, but there is a much larger part which 

 is regarded as insoluble under ordinary atmospheric conditions. How 

 is this supposed insoluble residue removed ? The sluggish stream which 

 meanders through the tangle of swamp vegetation that nourishes on the 

 moist floor of the basin is capable of transporting but a small percentage 

 of the waste from the surrounding slopes. This waste is being carried 

 down continually, and if the stream cannot remove it mechanically it 

 must remain upon the bottom of the basin or be carried away by 

 solution. Since the observed baselevels show little indication of de- 

 position upon their surfaces, which is generall}^ composed of rocks in 

 situ, we are forced to the conclusion that much of this so-called insoluble 

 waste is in reality soluble under certain conditions which appear to be 

 present during the process of baseleveling. 



Evidence of Solution at Baselevel afforded by etched Pebbles 



and geodes. 



The occurrence of etched pebbles of vein quartz and of etched silicious 

 geodes, as described in the preceding paper, would seem to indicate that 

 under certain conditions of weathering even the most resistant form of 

 silica is readily dissolved, while the more soluble forms are acted upon 

 almost as readily as limestone under ordinary atmospheric conditions. 



The conditions under which the pebbles of vein quartz, found by 

 Mr Hayes on Clifty creek, Tennessee, were etched is very similar, appar- 

 ently, to those which prevail upon a baseleveled surface. Clifty creek is 

 upon the Cumberland plateau, which is formed by the horizontal beds 

 of Coal Measure sandstones and conglomerates. Upon this surface the 

 streams are sluggish, often obstructed by a heavy growth of vegetation, 

 and in many respects the conditions simulate those which must have 

 prevailed when this same plain was near sealevel. During the summer 

 season the water of these streams is loaded with the products of decaying 

 vegetation to such an extent that it becomes brown in color and disagree- 

 able to the taste. If the swampy condition of the plateau adds to the 

 water of its slowly moving streams such a strong solvent, what must have 

 been the character of the water of the streams which meandered over the 

 same surface when it stood at sealevel and was covered with the rank 

 growth of vegetation which must necessarily have prevailed during the 

 Cretaceous cycle ? 



The etched pebbles found by the writer at the base of the Nuttall cliff 

 on New river are apparently the result of conditions similar to those 



