34 NEW YORK STATE MUSEUM 



what the same character.^ So it is evident that the thinning of 

 the Trenton eastward across the territory included in the map 

 sheet, is only a local exhibition of a more widely extended 

 feature. 



Ripple marks in the Trenton. A mile above the mouth of the 

 creek which empties into West Canada from the east 2 miles 

 above Middleville is an interesting exhibition of ripple marks, 

 interesting because of their comparative rarity in limestone 

 formations. The Trenton section up this creek is a very interest- 

 ing and complete one. The ripple-marked horizon is about 100 

 feet above the base of the Trenton and in slaty limestones which 

 approach the passage beds in character. The stratum has a 

 slight westerly dip and the creek flows down the dip for several 

 rods, so that the rippled surface is widely exposed. The crests 

 of the ripples are from 9 to 15 inches apart, so that they are con- 

 siderably broader than the usual ripple marks in sandstones, and 

 the troughs are depressed from 1 to 3 inches below the crests. 

 They run nearly at right angles to the course of the stream, 

 which is thus flowing down a gently inclined, corrugated surface. 

 There results from this a number of little, local eddies in the 

 water, which are strongest in the lowest sags of the troughs, 

 riere the water is beaten up into foam, forming globular masses 

 up to 6 inches in diameter, which rotate in the eddying water 

 and give a very striking appearance to the stream. Varying dip 

 brings this layer to daylight again some 50 rods farther up 

 stream. Not far beneath is a knobby, black limestone layer, full 

 of nodules of chert, containing much pyrite (marcasite), and 

 holding a great number of specimens of a single species of fossil 

 (Orthoceras). 



irtiea shale. This formation consists throughout of black, or 

 blue black, somewhat carbonaceous, fine mud shale. It is mostly 

 very thin splitting (or fissile), this being specially true above. 

 In the lower portion more solid bands are not infrequent, and the 

 shale is usually somewhat calcareous, thin bands of slaty lime- 

 stone being of frequent occurrence in the basal portion, though 



^Prosser. Op cit p.638-40. 



