8 I 8 MYRON L. FULLER 



the conglomerate at other points in Pennsylvania and described 

 by Mr. Arthur Winslow z are of similar origin, the only work of 

 solution apparently being the removal of the cement binding the 

 grains together. The disintegration of the conglomerate into 

 sand likewise appears to be unaccompanied by solution, except 

 that of the cement. 



Where the etched surfaces are fully exposed to the action of 

 the weather, as on the upper surfaces of ledges, they are, so far 

 as known, always bleached to a gray or white color, but where 

 they are more or less protected, as on the under sides of over- 

 hanging ledges, they are almost invariably stained with iron. It 

 is a well-known fact that the action of the humic acids is accom- 

 panied by a leaching of the iron constituent, or at least a 

 conversion of the iron to the ferrous state, in which it is ordi- 

 narily inconspicuous. The oxidized condition of the overhang- 

 ing surface would seem, therefore, to indicate that the etching, 

 if due to the action of the organic acids mentioned, is not going 

 on at the present time. The portions of the bowlders in contact 

 with the humus of the soil, though not etched, are distinctly 

 bleached. 



Summary of evidence. — The evidences that the etching prob- 

 ably took place in the instances described in the interior of the 

 conglomerate at some past time rather than at the surface under 

 present conditions are as follows : 



i. Etching has been noted about vegetable remains at dis- 

 tances of several feet from the nearest exposed surface, showing 

 that the solution is not a superficial feature. 



2. Bedding planes extending throughout bowlders of several 

 feet in diameter are frequently etched throughout, indicating the 

 penetration of the solvent to distances of at least a number of 

 feet from the surfaces. 



3. The continuations of horizontal etched surfaces, both on 

 the upper and overhanging portions of ledges, frequently ex- 

 tend up to and disappear into the mass of the rock, the exposed 



1 " Peculiarities of the Weathering in the Pottsville Conglomerate," Science, Vol. 

 Ill, pp. 12-14. 



