ETCHING OF QUARTZ IN CONGLOMERATES 819 



parts, in fact, apparently being portions of much larger surfaces, 

 reaching well into the interior of the rock mass. 



4. The etched surfaces, except those about the vegetable re- 

 mains, appear generally, if not always, to be confined to princi- 

 pal or to cross-bedding planes, or at least to joints, or other 

 planes of separation, such as might have afforded a passage for 

 solutions through the rock. The general absence of etching on 

 surfaces other than the types mentioned, especially on the 

 exposed exteriors of the masses, strongly suggests that the 

 etching was internal. 



5. The lack of bleaching on many of the etched surfaces 

 shows that the etching is not the result of organic solvents act- 

 ing at the present time, and affords negative evidence in favor 

 of internal solution. 



Co?iditions during the etching. — On examining the etched sur- 

 faces, it is found that only the immediate exterior is affected, 

 the pebbles and sand grains being pitted or planed down to a 

 general surface, without there being, in most cases, the slightest 

 evidence of solution of the cementing materials (Fig. 3). This 

 evidence tends to show 

 that the rocks were con- 

 solidated when the etch- 

 ing took place, and prob- Fig. 3. — Diagrammatic section showing charac- 

 ably indicates rapid ter of etched surfaces of conglomerate. (C. W. 



action of the etching Hayes > GeoL Soc - Am - BulL > Vol-VIIL, p. 217.) 

 solutions, for if the rocks were open and porous, as they would 

 have been before consolidation, or if the solutions passed 

 through them for considerable lengths of time, it seems almost 

 certain that the solutions would have penetrated for some dis- 

 tance into the body of the rocks and would have produced an 

 internal etching or disintegration of the portions adjoining the 

 bedding or other planes along which the solutions passed. The 

 existence of small open cavities about the vegetable remains is 

 also probably to be regarded as evidence of the consolidated 

 condition of the rock at the time the solution took place. 



If the internal nature of the etching of the conglomerate is 

 admitted, the question arises as to whether it occurred while the 



