REPORT OF THE STATE PALEONTOLOGIST 1902 983 



glomeritic and the upper part a coarse, cream-colored sand- 

 stone that weathers white on exposure. It is almost always 

 strongly cross bedded. The pebbles are well rounded and in 

 contrast to the flattened or discoidal pebbles of all of the under- 

 lying conglomerates in the region are predominantly ovoid in 

 shape so that the Olean is frequently referred to as the " round 

 pebble conglomerate." While flat pebbles do occur in it, yet 

 the proportion of round or ovoid ones is so great that the 

 distinction is good. These pebbles vary in size up to two op 

 three inches in diameter though the average diameter is some- 

 what less. Most of them are of vein qua rtz ; a few are of a hard, 

 dark gray slate; none are of red jasper. 



They are loosely embedded in a very arkosic sandy matrix, 

 in portions of which there is considerable iron which has formed 

 thin limonitic streaks or crusts through the rock and resists 

 disintegration much better than the arkosic cement does. 



Etched quartz pebbles. Pebbles of vein quartz embedded in 

 surfaces made of such limonitic crusts are frequently found 

 much etched or corroded. The only part played by the limonitic 

 crust is the holding of the same pebbles exposed on its surface 

 for some time till the etching agent has had time to greatly 

 corrode them. The nature of the etching agent is not certainly 

 known. It is generally thought to be some one of the humic 

 acids that result from plant decay. 



The best examples of such etching seen in the region by the 

 writer are in shallow depressions in which water stands after 

 a rain on the upper surface of the blocks that make up the 

 Genesee rock city. These huge blocks are on the top of a 

 high crest in a field with only one tree near that rises above 

 them. The upper surface of the blocks is bare except for a 

 very few submicroscopic plant forms which may possibly by 

 their decay furnish a corroding agent, though this impressed 

 the writer when examining them as not being an adequate 

 cause. 



The next best example of etching is found at Olean rock 

 city. Here both the cause and one rather diagnostic step in 

 the process seem more satisfactorily determinable. On the 

 under surface of overhanging portions of the rock so situated 



