58 NEW YORK STATE MUSEUM 



fault between the two is attestisd by the contact in Spruce creek^ 

 and by the study of the abundant outcrops on all sides. The 

 Beekmantown rocks are quite sandy, and yet strongly calcareous 

 (or rather dolomitic, effervescing only slightly with cold, but 

 abundantly with hot acid). They contain numerous pebbles, not 

 only of quartz but also of gneiss, identical with the white, 

 quartzose Grenville gneiss of the hill. Moreover, these pebbles 

 are considerably more numerous in the uppermost Beekmantown 

 layers than in those below, for the evident reason that the ex- 

 posed i)ortions of the lower la^^ers are at a greater distance from 

 the pre-Oambrian rocks than is the case with the upper ones, that 

 is, the pebbles increase in number with approach to the old shore 

 line, as they would be expected to do. The accompanying sec- 

 tion, drawn to scale, shows the actual conditions as observed, and 

 also by dotted line the approximate position of the pre-Cambrian 

 slope, the base on which the Beekmantown was deposited. The 

 section seems to the writer to be decisive as to overlap. 



Pig. 12 Section near Diamond hill showing overlap of Beekmantown on pre- 

 Cambrian. The Beekmantown strikes n. 45° w., dip 5 " s. The pre-Camhrian rocks 

 strike n. 80° w., with low northerly dip. 



This overlap of the Beekmantown denotes a j^rogressive sinking 

 of the immediate district during Beekmantown time. Its succes- 

 sive layers from base to summit must rest in turn on the old rocks, 

 after which the Trenton rests thereon. There is no known locality 

 in northern New York where the Utica may be found resting un- 

 disturbed on the old surface, the reason being that erosion has 

 everywhere cut below this horizon and removed every scrap of 

 the Utica from such situation. But there seems no reason to 

 doubt that the progressive subsidence continued intermittently 

 during Lower Silurian time and for an unknown length of time 

 thereafter. 



