GEOLOGIC FORMATIONS OF NEW TOEK 151 



Generally speaking, the lowest of these groups lies conform- 

 ably upon the strata of the Hudson river group, — the uppermost 

 of the Lower Silurian, — though in eastern Albany county the 

 Hudson river shales are much disturbed. 



In regard to this relation it has been said by Dana a : ' Oases 

 of intervening erosion may be found, for every period loises by 

 erosion a large part of its deposition in the. supply of material 

 for the beds of the following period.' 



Oneida Conglomerate 



The Hudson river group is covered in many places by a bed 

 of 'conglomerate consisting chiefly of coarse sand and rounded 

 pebbles of quartz, cemented together into a firm mass. Being 

 well developed in Oneida county south of Utica, it has received 

 its name from that of the county. 



It is the base of the Lower Silurian system. In central New 

 York it is but a few feet in thickness, and indeed seems to be 

 entirely wanting in many places; but in the lower Hudson val- 

 ley it swells to a thickness of .several hundred feet and south- 

 west of Eondout forms the Shawangunk mountain from which 

 it receives the name of Shawangunk grit. From this place its 

 upheaved edges may be traced in the range of hills southeast 

 of the Delaware and Hudson canal and parallel to it, and the 

 same rock forms most of the mountain range of the Kittatinny 

 or Blue Bidge, along which the Delaware flows from Port Jervis, 

 where it leaves New York, to the famous Delaware Water Gap 

 where it cuts through the barrier. From this point, its edge 

 ranges southward to Virginia. No fossils have yet been dis- 

 covered in it: indeed the rolled and worn condition of its ma- 

 terials would indicate that it was formed under agitated waters, 

 which did not allow the growth or preservation of organic 

 forms, i 



The well known summer resort of Lake Mohonk is on the 



Shawangunk grit. 



The 'Bensselaer plateau/ in Bensselaer county, is an ex- 

 tensive outcrop of greenish conglomerate, resting conformably 



a Man. Geol. pp. xxx 



