1052 



NEW YORK STATE MUSEUM 



Ten feet lower, or from 12 to 13 feet below the base of the 

 upper Stromatopora bed, is a third one, averaging 2 feet in 

 thickness. This has the aspect of a curly or concretionary rock, 

 is of a darker color than the inclosing Manlius, and often highly 

 crystalline. The structure of the Stromatopora appears on 

 weathered faces only. The bed occasionally thins and then 

 swells out again but does not exceed 2 feet in thickness. Its 

 lower and upper contact surfaces are very irregular, and a 

 certain amount of erosion (probably contemporaneous) appears 

 to have occurred before the deposition of this bed. This is 

 indicated by the wedging out of a 2 foot bed of Manlius lime- 

 stone just below the bed, as shown in the annexed figure. 



Both the lower and mid- 

 dle Stromatopora beds and 

 the intervening rock are fis- 

 sured and veined with cal- 

 cite, which is often coarse- 

 ly Crystalline. A Certain Fig - 11 Dia S ram oi Part of Stromatopora bed 

 J in city quarry, Hudson, showing the thinning out 



amount Of Slickensiding has of ^limestone layer beneath it 



also occurred, showing slight readjustment of the strata. 



In the southern end of the quarry over 40 feet of the Manlius 

 were at one time exposed without reaching the " Hudson river." 



Contacts between Manlius and Coeymans. The contact between 

 the Manlius and Coeymans, or the Siluro-Devonic contact, is 

 shown in numerous exposures on the mountain. From the ex- 

 posure at the head of the aqueduct in Greenport it can be traced 

 westward for a short distance, when it disappears under drift. 

 Scattered ledges of both upper and lower rock allow its approxi- 

 mate determination to the city quarry, where, as noted, it is 

 again well shown. Beyond that it is traceable south westward 

 and southward in the cliffs and on the slope of the hillside, with 

 some inter in ittances, though seldom with a well exposed contact, 

 to the Jonesburg road. On the south edge of this, after crossing 

 the meadow land, and halfway up the hill in a low cliff on the 

 right, is a good exposure of the upper Manlius beds with the 

 capping Stromatopora layer. The Coeymans is exposed in the 

 road a short distance up the hill. The dip of the strata is ll°s.e., 

 the strike n. 30°e. For some distance southward from this 



