MUSEUM OF COMPARATIVE ZOOLOGY. 315 



north end of the Quarry Hill : they arc sandy limestones, without fossils 

 as far as observed, and not more than five or ten feet thick between char- 

 acteristic Hudson lliver sandstones and shaly layers of the Waterlime. 



There is no distinction attempted on our map and sections between 

 the Waterlime and the Tentaculite limestone : all the calcareous layers 

 below the knotted strata of the Lower Pentamerus are marked by a 

 single color. Professor Hall (Paleontology of New York, III. 386) 

 describes the Waterlime as being of " gray or drab-colored surface and 

 darker interior color, and almost destitute of fossils " ; while the Ten- 

 taculite is " a thinly bedded blue or black limestone, abounding in 

 certain organic remains." These characters are easily recognized. The 

 total thickness of seventy feet was measured on the eastern slope of the 

 Quarry Hill, from the uppermost sandstone to the lowest knotted lime- 

 stone. At Austin's Mills tlie measure would be less. The suljdivisions 

 of the Tentaculite, as described at Rondout (see Lindsey and Dale, as 

 below), are here clearly made out. Some ten feet of fossiliferous lime- 

 stone are followed by the Stromatopora layer, of one or two feet thick, 

 with numerous sponges a foot or a foot and a half in diameter (fig. 4) ; 

 next above come twelve feet of fine Ribbon limestone, in even parallel 

 layers, shown by alternating bands of lighter and darker color, often as 

 thin as one twentieth of an inch ; then comes the coarse Lower Penta- 

 merus, but about ten feet above its base there is a band of Ribbon 

 limestone again, one or two feet thick. • The even lines and smooth 

 gray weathered surface of the Ribbon limestone frequently serves as a 

 well-determined horizon, outcropping on the slope of the ridges made 

 by the Lower Pentamerus. 



The fossils of the Tentacidite limestone commonly seen are a Leper- 

 ditia, a Tentaculite, Orthis plicata, and a Turritella {?). The first two are 

 very common on certain layers. The thickness of the Waterlime and 

 Tentaculite has already been mentioned as seventy feet or less. These 

 two divisions of the limestone group are well seen — at least their upper 

 members — at many points along the front of the Kalk Berg, around 

 the synclinal outlier opposite Austin's Mill, and at the head of the 

 southern anticlinal valley. 



The change to the coarse, heavy, knotted layers of the Lower Pen- 

 tamerus is accomplished within two or three feet. With this comes 

 the frequent occurrence of dark chert in irregular masses up to six 

 inches in diameter. The fossils easily found are Pentamerus galeatus 

 (beaks are very common on weathered slopes in the soil) and Atrypa 

 reticularis : both are common. The thickness measured about eighty 



