302 AUGUST F. FOERSTE 



the presence of raindrop impressions or of any other evidences 

 suggesting deposition under shallow-water conditions. 



Perry next calls attention to the exposures at the Ridenour Mill, 

 on Little Fourmile Creek, about 7 miles north-northwest of Oxford, 

 where numerous layers in the upper part of the Waynesville and 

 lower part of the Liberty divisions of the Richmond group are 

 ripple-marked. 



Next, Perry cites the presence of mud-cracks from a locality 

 near Moores Hill in Dearborn County, in Indiana, presumably 

 from the Waynesville division of the Richmond group. And, 

 finally, he alludes to the well-known ripple-marks in the upper part 

 of the Cynthiana formation, at Ludlow, Kentucky. 



Now, whatever may be the opinion concerning the value of 

 ripple-marks as evidence of shallow-water conditions, there can 

 be no difference of opinion as to the evidence presented by rain- 

 drop impressions and mud-cracks. However, the presence of 

 raindrop impressions and of mud-cracks must be fully proved. 

 This the present writer has been unable to do. 



Specimens formerly interpreted by him as exhibiting rain- 

 drop impressions he now regards as ripple-marked, irregular 

 ripples of short amplitude crossing at various angles, leaving 

 intermediate more or less circular hollows. If anyone has clear 

 evidence of the presence of raindrop impressions in Cincinnatian 

 strata, this evidence should be published, accompanied by clear 

 illustrations. 



As regards the presence of mud-cracks, the present writer has 

 seen many occurrences of structures suggesting mud-cracks, but 

 has come to regard their origin from exposure of mud-flats to aerial 

 conditions as extremely doubtful. 



When mud exposed to the drying effects of the open air cracks, 

 it not only tends to pull apart at the cracks, but the upper, more 

 rapidly drying part tends to pull away from the part beneath. 

 Frequently the cracked surface becomes sufficiently hardened to 

 remain more or less intact when the next tide proceeds to cover it. 

 This causes the subsequently deposited material to settle in part 

 in the cracks, and frequently the part rilling the cracks is sufficiently 

 different to be readily distinguished from the original mud deposit. 



