wai.(ott.] NIAGARA FALLS TO NEW YORK CITY. 4fil 



a spar of bedded Algonkian gneiss crosses tlielineof the railroad; a 

 tine geologic section is exposed along the cuts and the Mohawk 

 River. 



The Onondaga, Niagara, and Clinton terranes have been fully- 

 described by the veteran geologist and paleontologist, James Hall, 

 and the two latter terranes are mentioned in this Guide as they are 

 seen in the canyon of the Niagara. The immediate subjacent forma- 

 tion, as itoccnrs in the vicinity of Utica, includes 800 feet of argilla- 

 ceous shales in which numerous sandy layers occur near the summit. 

 The lower 710 feet is the Utica formation, and the upper IK) feet the 

 equivalent of the Lorraine shales and sandstones. The Trenton lime- 

 stone has a thickness of about 150 feet at Little Falls, and the imme- 

 diately subjacent Calciferous sandrock, 190 feet. A thin bed of sand- 

 stone and shale, just above the Algonkian gneiss has been referred to 

 the Upper Cambrian (Potsdam sandstone) zone, but on evidence that 

 is not conclusive. A fine section of the bedded Algonkian gneisses is 

 shown in the cliffs below the sandstones, and in the river, at the upper 

 end of the narrows, a massive gneiss or granite is to be seen. The 

 almost horizontally bedded Algonkian strata, although crystalline, 

 have frequently been taken to be the downward extension of the super- 

 jacent Calciferous formation. Other exposures of the Algonkian, 

 Calciferous, and Trenton terranes occur in the cliffs of the northern 

 side of the valley, between Little Falls and South Schenectady, while 

 with slight exception the hills on the south side are formed of the 

 Utica shale, with the Trenton limestones at the base. 



Turning southeast from South Schenectady the road enters the 

 valley of the Hudson and an area where I he geologic structure is 

 entirely unlike that passed over from Niagara Falls to South Schenectady. 

 The Silurian (Ordovician) rocks are upturned, compressed, and more 

 or less broken by the westward thrust of the masses of rock dis- 

 turbed by the crumpling and folding of the strata of New England. 

 Within the valley there remains to be solved one of the most compli- 

 cated local geologic problems in North America geology. The higher, 

 outer western sides of the valley are formed of the horizontal Lower 

 Helderberg limestones, with a thin band of the Niagara corralline 

 limestone, beneath which a great thickness of alternating sandstones 

 and shales extend down to a limestone, found in deep wells at ii,47o 

 feet beneath the upper limestone. It is this series of shales and sand- 

 stones that are so plicated and altered in the valley to the eastward. 

 As far as known there are no exposures of the undisturbed strata below 

 a point 000 feet beneath the Helderberg limestone. The Upper 000 feet 

 exposed has been correlated with the Lorraine, the limestones at the 

 bottom of the dee}) wells with the Trenton, and the strata between with 



