346 C. D. WALCOTT — THE TERM "HUDSON RIVEB GROUP." 



starting 595 feet vertically below the base of the Lower Helderberg limestone. 

 It is reported that the strata passed through were gray shales and alter- 

 nations of gray and black slates, which in places were quite calcareous and 

 contained occasional thin beds of sandstone. At the depth of 2,**o feet. 

 the Trenton Limestone was struck ; adding to this the 595 feet of shales and 

 sandstones between the mouth of the well and the base of the Lower Helder- 

 berg limestone, we have a total thickness of 3,475 feet for the strata between 

 the Lower Helderberg and the Trenton limestone on the west side of the 

 valley of the Hudson.* This section is of great interest, as it proves be- 

 yond question that there is a great series of shales and interbedded sandstones 

 between the Lower Helderberg and the Trenton limestone in the valley of 

 the Hudson. If we go down the valley of Norman's kill until the upturned 

 rocks are met with, we shall have little doubt that the latter are equivalent 

 to a portion of the section passed through by the well. That the graptolite- 

 bearing beds of the Hudson valley are low in the section is proved by the 

 fact that no graptolites, with the exception of one or two wide ranging 

 species, are known in the upper portion, immediately along the base of the 

 Helderberg mountain. 



If the geologist follows along the contact of the Hudson series with the 

 Lower Helderberg to the Schoharie kill, and then proceeds down the stream 

 to the valley of the Mohawk, he will pass over a large portion of the section 

 penetrated by the well, and, in the valley of the .Mohawk, find that the 

 series rests conformably upon the Trenton limestone, and that the base is 

 formed of dark Utica shales. 



I next studied the strata on the eastern side of the Hudson, in Washington 

 and Rensselaer counties, and found a development of rocks characterized 

 by the graptolites of the Hudson terrane. They may be separated into 

 three divisions on the bases of lithologic character and geographic distribu- 

 tion: 1. The tlark argillaceous shales of the area between the western border 

 of the county along the Hudson river and the great fault that skirts the 

 western base of the range of hills separating the hilly country from the 

 low, tlat land of the river valley. 2. The Bilicious cherty bed.-, the green 

 and red .-lates. ami the dark argillaceous -hales that occur, associated with 

 them, over the central and interior portions of Washington county. •">. The 

 dark argillaceous -hale- and green hydromica schists of the still more eastern 

 Taconic range. There is not Bpace for a full description of the rocks. 

 They are largely formed of -hale- and sandstones and Bilicious slates, (lip- 

 ping to the eastward at an average angle of 10°. < mi<- Bection measured in 

 Greenwich, Washington county, -jive- a thickness of 2,600 feel ; the grapto- 

 lites occur loit feet and 1,700 feet above the base, and over the upper 



I hi iting to theKnowen>vilIe and Knox wells are taken from h paper by Mr. Charli 



urner "On the Petroleum and Natural Gas In New Vorh State," 1888, pp. i- 



