ETCHING OF QUARTZ IN CONGLOMERATES 82 1 



view that the solvent had its origin in the vegetable matter of 

 the rock itself, that it was concentrated along bedding planes or 

 other passages in the rock, and that it was only where so con- 

 centrated that visible etching was produced. The etching is not, 

 however, to be necessarily considered as confined to those parts 

 of the rock abounding in vegetable remains, the solutions prob- 

 ably being conducted by the bedding or other planes to portions 

 remote from the original source of the solvent. 



Conclusions. — The observations have been insufficient to war- 

 rant broad generalizations, but the evidence, though not so de- 

 cisive as might be desired, seems to favor, as far as the Blossburg 

 locality is concerned, the conclusions given below. It is not 

 probable, however, that they will hold for the occurrences at all 

 localities. 



1. The etching has not taken place under existing conditions. 

 This is indicated by the unetched character of the portions of 

 the rock exposed to the atmosphere or to the humus of the 

 soil, and by the present oxidized condition of most the etched 

 surfaces. 



2. The etching is an internal feature, as is indicated by the 

 etching about the plant remains, by the etched interiors of 

 detached blocks, and by the extension of etched surfaces into 

 the mass of the rock. 



3. The etching took place after the rock was fully consoli- 

 dated, as is shown by the fact that it is confined to the immedi- 

 ate walls of the bedding or other planes, the etching solutions 

 failing to penetrate the rock or even to dissolve the cementing 

 material except very locally. 



4. The etching is believed to have taken place while the rock 

 was moderately deeply buried, the depth, however, probably not 

 exceeding 500 feet, this being a common limit of the circulation 

 of fresh water below the general surface, as shown by the 

 numerous oil and gas drillings in Pennsylvania. 



5. The active solvent was probably an organic acid and was 

 most likely derived from the vegetable remains within the rock 

 itself. 



Myron L. Fuller. 

 U. S. Geological Survey. 



