21Y 



The ripple marks have rounded crests and hollows, the slopes on the 

 two sides of a crest being in general symmetrical about the axis. The 

 mean distance from crest to crest is approximately uniform for the series, 

 and the average for twenty such distances is found to be 2.63 feet. The 

 average depth of lowest part of troughs below crests is one and one-half 

 to one and six-tenths inches; total number of crests exposed is forty. The 

 ripple marks in the up-stream portion of the exposed area, constituting 

 the majority of the number named, extend entirely across the bed of the 

 stream; in the down-stream portion, a part of the ripple marks have been 

 woni away by erosion of the stream, leaving the crests only near the 

 margins. 



The stratum which has the ripple marks is about three inches in 

 thickness, measured to top of crests; the bottom of this layer is as nearly 

 plane as are the surfaces of the other layers of Hudson River rock in this 

 locality; that is. no indication of the undulations (which are on the upper 

 surface), is found on the lower side of the layer; and this layer containing 

 the ripple marks is not noticeably different in thickness from that of the 

 other layers of the same formation just above or just below it geologically. 



Ihe ripple-marked stratum, in the southwesterly (up-sti;eam) direction, 

 disappears beneath other strata of Hudson River limestone. This stratum 

 above, when brolcen up and removed, showed a layer of blue shale or mud, 

 filling the hollows, and bai'ely covering the crests of the ripples; the ripple 

 marks, however, were as clearly defined where the upper stratum was 

 broken away as in the exposed portion farther down the stream. 



The right bank of the stream is steep and higher than tlie left bank; 

 and here the Hudson River rock outcrops up to a height seven or eight 

 feet above the water; the upper stratum of Hudson River rock in this 

 vicinity is estimated at forty feet above the ripple-marked stratum. The 

 left bank is a part of a flood-plain. At one point a trench was dug back 

 from the water's edge on this side. When soil, sand and gravel were re- 

 moved, the ripple marks were found clearly defined as far as the digging^ 

 extended, some of the blue shale being found adhering to the surface. 



The under side of the ripple-marked stratum is paved in nearly every 

 square inch with well-preserved fossils, consisting In far tlie greater part 

 of Leptaena sericea. These are associated with Raflnesquina alteniata, 

 Orthis occidentaUs, Rhynchotrema capax, and a veiT few other brachiopods. 



Let it be understood all the time that the under surface of this layer 

 is entirely flat. The upper, or rippled surface, is very smooth and shows 



