NEW YORK STATE MUSEUM 



that they could not be wet by rain or receive drippings from 

 any surface above were found many small well etched pebbles 

 of vein quartz. These under surfaces of the rock were very 

 appreciably moist, however, even on a hot summer day. This 

 moisture was derived partly by seepage of contained moisture 

 down through the loosely cemented rock itself and partly by 

 -direct condensation of moisture from the atmosphere, since 

 from their sheltered position these surfaces remain quite cool 

 even on the hottest days. If due to an organic acid of decompo- 

 sition, this acid must have reached the etched under surface 

 by soaking through some 30 or 40 feet at least or rock. Why 

 it has not attacked and corroded the many quartz pebbles 

 passed on its way through the rock, but has preferred to wait 

 till it has reached the under surface before becoming chemically 

 active seems explicable on the theory advanced by Dr C. W. 

 Hayes 1 . The acid was probably humic and so was compara- 

 tively inert till it had come into free contact with the 

 atmosphere on reaching the underside of the ledge, where it 

 absorbed nitrogen from the air forming azohumic acid which 

 has a strong affinity for silica and at once began corroding the 

 quartz pebbles. These somewhat exceptional conditions at 

 Olean rock city seem most readily explicable on this theory 

 and they in turn lend additional strength to the theory itself. 



Disintegration of the Glean is as a rule very rapid and talus 

 slopes occur everywhere so that the base is rarely or never 

 exposed. Numerous well borings have penetrated it, however, 

 on the Olean quadrangle and give an accurate measure of its 

 thickness there which is usually between (>0 and TO feet, though 

 in one well it is 90 feet. It occurs on the highest hilltops in the 

 southern part of the two quadrangles, in a number of small 

 detached areas and is well known southward in McKean county 

 and westward in Warren county in Pennsylvania. 



Above the Olean conglomerate at rock city are found a few 

 feet of thin, sandy, ferruginous shales in which some years 

 ago a thin coal bloom was exposed in grading a road. It also 

 belongs to the Pottsville. 



1 Hayes, C. W. Solution of Silioa umVr Atino-pheru- Conditions. Geol. Soc. 

 Amer. Bui. 8:213-20. 



