204 



to each other. It is observed that, while the crests are not straight, but 

 more or less cnrving in their (nitline, they are essentially parallel. 



On Doe Run, about two miles from Brooksburg, a ripple marked lime- 

 stone is exposed in the creek 1)ed, over a space of a few square yards. The 

 trend of crests here is approximately N. 45° E.; wave length, thirty-three 

 to thirty-six inches; depth of trough, three inches; thickness of limestone, 

 three to live inches. The vertical distance of this series of marks below 

 the Clinton formation could not l)e determined so readily as in the other 

 cases, since the outcropping Clinton is not found witliin a distance of 

 several miles. An approximate vertical distance of 380 feet below Clinton 

 was reckoned on the basis of an observed westerly dip of ten feet to the 

 mile of the Clinton formation in other parts of the county. 



Tlie main facts in regard to these ripi)le marks are placed in tabular 

 form below. 



These Hudson limestone ripple marks are exceptional in that ripple 

 marks are unusual in limestone, lieing found in sandstones and shales 

 chiefly. They are exceptional also in the fact tliat they are of such large 

 size. A few inclies usually measm-cs the distance from crest to crest of 

 ripple marks. Since a ripple is a small wave, these limestone markings 

 might well be called wave marks, were tliat term not preoccupied. These 

 ripple marks indicate essentially seashore conditions during the period 

 occupied in depositing some otM) feet of Hudson rocks and that the condi- 

 tions finally resulting in the Cincinnati Ceanticline or uplift at the close 

 of the Ordoviciaii. had long been present. Tlie trend of these marlvS from 

 N. 10° E. to X. 7."»° E'.. goes far towards indicating prevailing winds from 

 the northwest or tlie southeast during that part of paleozoic time repre- 

 sented in the d('i)osition of these rocks. 



