PALEOZOIC TIME — DEVONIAN. 



605 



Middle Devonian. Still farther east, along the Hudson Kiver valley, the 

 Catskill formation occupies the whole of the Upper Devonian interval." 

 The beds show that the region of their depositions was invaded here and 

 there at times by fresh waters from the bordering hills. 



In the Catskill Mountain region the Catskill rocks are to a large extent 

 the summit rocks and have a thickness there of 3000 feet. Marking them, 

 as is usual, by their coarse sandstone character and red color, they extend 

 southwestward into Pennsylvania, along the course of the Appalachian 

 trough, from Port Jervis, N.Y., to Fulton County, and have a reported 

 thickness, in this part of the state, of 4500 to 7000 feet ; 3430 at Port Jervis, 

 4000 to 5300 in Monroe County, Pa., 7544 near Mauch Chiink, 6000 in Perry 

 County, and 3900 in Fulton County, In Fulton County, Chemung fossils 

 have been observed in the so-called Catskill beds by J. J. Stevenson, through 

 the lower 900 feet, reducing the thickness of the so-called Catskills at that 

 point to 3000 feet. West of the above-mentioned line, the reported thickness 

 diminishes ; in southwestern Bedford County, it being but 2000 feet, and 

 only a few feet in western Somerset County. 



Eastern Xew York and Pennsylvania continued to be for a long time a sea- 

 border region, undergoing the subsidence required for thousands of feet of sea- 

 shore deposits, because here lay the border of the Appalachian geosyncline. 



The Portage group was early called the Niinda group, from this early name of the 

 village of Portage, situated on the banks of the Genesee Elver, where the beds occur. 

 The Genesee shale is finely displayed at the opening of the gorge of the Genesee at Mount 

 Morris ; and it also forms high cliffs above the TuUy limestone along the borders of 

 Cayuga and Seneca lakes. The concretions occurring in the rocks sometimes contain min- 

 eral oil, and a soft substance looking like spermaceti. The region of the Portage beds in 

 New York is famous for its waterfalls. 



On the Genesee Kiver, the group includes, above the Genesee shale, (1) the Cashaqua 

 shale, and the Gardean shale and sandstones, the Naples beds of J. M. Clarke ; and 

 (2) the Portage sandstones. The Portage beds of western Pennsylvania are so deeply 

 buried that their thickness is unknown ; the drillings for oil do not reach down to them. 



The Ithaca grouj) abounds in ripple-marks, mud-cracks, calcareous concretions, and 

 cone-in-cone forms. It is referred by Hall to the Chemung series. 



Prosser has deduced from the many drillings in western New York, and the observa- 

 tions of Hall, H. S. Williams, and others, the following section for the region not far 

 west of the Genesee River, near Rochester : — 



Feet 



Wolf Creek Conglomerate . 300 



Chemung (to 1450' depth) . 1150 



Portage 900 



Genesee shale 100 



Hamilton (to 3200' d.) . . • 750 



Marcellus shale 50 



Corniferous .... 

 Lower Helderberg ? . . 



} 



150 





Feet 



Salina? (to 4000' d.) . . 



600 



Niagara and Clinton . . 



250 



Medina 



1158 



Hudson, Utica .... 



598 



Trenton (to 6960' d.) . . 



954 



Calciferous ? (to Archaean ?) 



137 



In Pennsylvania, in Perry County, the Chemung is 3300' thick, and the Catskill 6000' 

 (Claypole) ; but the latter contains in its lower third some Chemung fossils. In Columbia 



