ETCHED CONGLOMERATE AND ETCHED PEBBLES. 217 



for when examined with a lens the projecting portions of the sand 

 grains, both large and small, are generally leveled off, forming with the 

 kaolinized feldspathic ma- 

 trix a more or less even 

 mosaic. 



The sectional view shown 



,. ,. . ., Figure i. — Section of Conglomerate showing etched 



on the diagram suggests the pebbles. 



form assumed by the faceted 



pebbles or glyptoliths described by Woodworth, Davis,and others* and 

 by them ascribed to the action of wind-blown sand. The latter, how- 

 ever, display certain well marked characteristics, which sharply differ- 

 entiate them from those above described. The sand-cut facets, even 

 w T hen most perfectly developed, are always slightly convex, or at least 

 never deeply concave. They approximate plane surfaces which, in 

 case several are present on the same pebble, intersect in more or less 

 definite straight lines, and finally they are always more highly polished 

 than other portions of the same pebble which display only the ordinary 

 water-worn surfaces. All of these characteristics, and particularly the 

 last, serve to distinguish the wind-carved surfaces from those produced 

 by the corrosion of a solvent. 



Analogous Cases of Solution of Silica. 

 etched pebbles from coal measure conglomerate of ohio. 



Some analogous cases of the solution of silica under atmospheric con- 

 ditions, only a part of which have been personally observed by the writer, 

 may be mentioned in this connection. 



At the Cleveland meeting of the American Association in 1853 some 

 specimens of the Ohio Carboniferous conglomerate were exhibited by 

 Professor Brainerd.f in which the impressions of the stems of plants 

 were as distinctly transmitted to the quartz as to the sand matrix. Pro- 

 fessor Brainerd argued on the evidence afforded by those specimens that 

 the pebbles were of concretionary origin, and that they had received the 

 impressions while still in a gelatinous condition. Professor Newberry,J 

 on the other hand, expressed the opinion that the pebbles had been dis- 

 solved away where they were in contact with the plant by means of the 



* J. B. Woodworth: Post-Glacial Eolian Action in Southern New England, Am. Jour. Sci., vol. 

 xlvii, 1894, pp. 63-71. W. M. Davis: Faceted Pebbles on Cape Cod, Proc. Bost. Soc. Nat. Hist., 

 vol. xxvi, 1893, p. 166. Max Verworn: Sandschlieffe vom Djebel Nakus, Neues Jahrb., Bd. i, hft. 3, 

 1896, pp. 200-210. 



f Jehu Brainerd: Origin of the Pebbles Quartz of the Sandstone Conglomerate and the Forma- 

 tion of Stratified Sand Rocks. Cleveland, 1854, pp. 16. 



J J. S. Newberry: Ohio Geol. Survey, vol. ii, part 1, 1874, p. 11 r. 



