INTRAFORMATIONAL PEBBLES IN RICHMOND GROUP 301 



is this true in the case of the larger pebbles, which apparently 

 have been transported only short distances. 



Moreover, there is no evidence of strong unconformities any- 

 where in the Richmond series of rocks. At no point has a layer 

 of rock been found to overlap the lateral margins of any of the 

 layers for even a vertical distance of 2 feet. Hence an origin from 

 anything like a cliff or coast or beach seems questionable. At 

 least there is no evidence of the presence of any cliff, coast, or 

 beach sufficiently close to the area in question to have furnished 

 the material for the pebbles. 



There was a tendency formerly to regard the presence of ripple- 

 marks as evidence of shallow-water conditions and as suggesting 

 the proximity of shore lines. This found expression in a paper 

 by Joseph F. James on the " Evidences of Beaches in the Cincin- 

 nati Group." 1 Here the ripple-marks in the upper part of the 

 Cynthiana formation, at Ludlow and West Covington, Kentucky, 

 opposite Cincinnati, and another set of ripple-marks about 300 

 feet above low-water mark in the Ohio River, presumably in the 

 upper part of the Eden formation, were interpreted as evidences 

 of the proximity of beaches. As further evidence of shallow-water 

 conditions during the deposition of various parts of the Cincinnati 

 group, the presence of raindrop impressions near the top of the 

 Cincinnati group was cited, but the exact location of the rock 

 bearing these raindrop impressions is not given. 



The impression that at least a part of the rocks of the Cin- 

 cinnati group were deposited in very shallow waters finds expres- 

 sion also in a paper by Nelson W. Perry on "The Cincinnati 

 Rocks; What Has Been Their Physical History?" 2 Here rain- 

 drop impressions are cited from the vicinity of Smiley's Dam, 2,2 

 miles southeast of Oxford, but 5 miles distant when approached by 

 the road. The dam is located on Fourmile Creek. The lowest 

 strata exposed belong to the Mount Auburn division of the Mays- 

 ville formation, and a mile westward the Dinorthis carleyi horizon 

 near the middle of the Arnheim bed is exposed at an elevation about 

 50 feet higher. Careful search by the present writer failed to locate 



1 Science, V (1885), 231. 



2 Am. Geol., IV, No. 6 (1889), PP- 326-36. 



