284 G. H. Smyth, Jr. — Corrosion of Quartz. 



and holds that the process has taken place at moderate depth 

 beneath the surface. 



Long ago, Newberry* regarded the impressions of plant 

 stems upon the quartz pebbles of conglomerate as due to 

 organic acids, and, as quoted by Bolton,f explained in the 

 same way the corrosion of quartz pebbles occurring in car- 

 bonaceous clay. 



As the present instances of corrosion show no connection 

 with unusual supplies of decomposing organic matter and alka- 

 lies, at the surface ; and as the conglomerate contains little, if 

 any, original organic matter, none of these explanations seems 

 applicable; but, unfortunately, no satisfactory substitute is 

 forthcoming. 



As already stated, the corrosion appears to be a superficial 

 process — a peculiar phase of weathering. To this may be 

 added the striking fact that, thus far, corroded pebbles have 

 been found only in the pyritiferous beds, though carefully 

 sought for in the overlying pure quartz conglomerate. 



Thus, corrosion seems to be dependent upon two conditions, 

 — presence of pyrite and weathering, — which suggests the con- 

 clusion that the products of the weathering of pyrite act as 

 solvents of quartz. But, so far as the writer is aware, such a 

 conclusion finds no support in the results of laboratory study ; 

 and an explanation of the phenomena must await further 

 investigation. 



It might be suggested that the corrosion is merely apparent, 

 not real, resulting from the weathering out of pyrite from 

 partly replaced quartz, thus leaving, as would evidently be the 

 case, a rough pitted surface. This simple explanation is not, 

 however, in harmony with the facts. The replacement though 

 greatly modifying the shape of small sand grains, perhaps even 

 completely destroying them in some cases, does not go deep 

 enough to materially change the shape of the larger pebbles, 

 upon which corrosion is conspicuous. So, while mere weather- 

 ing out of pyrite would give a rough surface, it would not 

 yield the deeply corroded pebbles. Furthermore, a surface 

 left by the removal of pyrite would be marked by depressions 

 corresponding in shape with the pyrite, and, thus, often 

 bounded by small plane faces, which is distinctly not the case 

 with the corroded pebbles. 



The rough surface left by the removal of pyrite would, of 

 course, favor solution of the quartz by any agent present, and 

 to this extent, surely, replacement is a factor in the subsequent 

 corrosion. 



The Oneida conglomerate, then, presents two types of solu- 



* Geol. of Ohio, vol. ii, pt. I, p. 111. 



+ Ann. N. Y. Acad. Sci., i, 1877, pp. 35-36. 



