482 



NEW YORK STATE MUSEUM 



To the south of the trough of the Mohawk valley we have first 

 the shales, followed in ascending series by the Medina and Oneida 

 sandstones. The shales and limestones of the Clinton formation, 

 the Niagara limestones, the rocks of the salt group, the Helder- 

 berg limestone, the Oriskany sandstone, the Onondaga limestone, 

 and finally the extended area covered by the Catskill and Che- 

 mung sandstones. The headwaters of Schoharie creek issue 

 mostly from the Catskill formation, although the extreme head- 

 waters flow from off the Oneonta sandstone, which, however, is 

 closely allied to the Catskill. The shorter streams on the south 

 side issue from the horizon of the Hudson and Utica shales, the 

 same as short streams to the north. 1 



The soils of a considerable portion of the Mohawk river catch- 

 ment area are consequently heavy and impermeable, and further 

 tend to give heavy runoffs at time of flood-floAv. 



As regards flood-flows in the lower Mohawk river, the stream 

 divides naturally at Little Falls. Below that point the flat area 

 is relatively more restricted, and the flood-flows probably larger 

 in volume than at Little Falls. We have already given particu- 

 lars of the highest flood at Rexford Flats, where the catchment is 

 3385 square miles. According to the Report on Water Power in 

 the Tenth Census, in an extreme flood which occurred about 1860 

 to 1865 there is stated to have been a depth of 12 feet of water on 

 the Cohoes dam, which is 1400 feet in length. If such a depth 

 actually occurred, the discharge may have been over 200,000 cubic 

 feet per second or at the rate of over 59 cubic feet per second per 

 square mile. The information at hand does not indicate a flow 

 over about 78,350 cubic feet per second or 2'.\ cubic feet per second 

 per square mile at the Rexford Flats dam. The. maximum, how 

 ever, in view of the foregoing, may be placed at a considerably 

 higher figure than this. 



Floods in Cayadutta end;. The maximum flood of this stream 

 near Johnstown is stated to have occurred in the spring of 1896, 

 at which time the flow was 2896 cubic feet per second (catchment, 

 40 square miles), or ai the rale of 72 cubic feet per second per 

 square mile. 



'Also soo statements regarding geology of Mohawk valley on p. 411. 



