HYDROLOGY OF NEW YORK 



1G5 



ent geologic formations. As regards quality of soils, Mr Yer- 



meule also says : 



It may be inferred that the kind of soil has much less to do 

 with the amount of evaporation than has the temperature. 



As regards the relation between geology and runoff, it is 

 undoubtedly complicated, although it is interesting to note that in 

 the State of New York streams which flow from the north into the 

 Mohawk river, after crossing over a narrow strip of Trenton lime- 

 stone and Calciferous sand rock, and which head in the Laurentian 

 granite of the Adirondacks, have larger flows than those coming 

 to the Mohawk from the south, which lie mostly in the horizon of 

 the Hamilton shales, the headwaters of some of them — as, for 

 instance, Schoharie creek — 'being in the sandstones of the Che- 

 mung and Portage groups. In their lower reaches they cross over 

 the sandstones and shales of the Hudson and Utica groups, with 

 narrow strips of Helderberg limestone, Oriskany sandstone, and 

 Onondaga limestone. 



However, there is another consideration. The headwaters of 

 the streams to the north of the Mohawk nearly all lie in a region 

 heavily timbered — some of it is still primeval forest — while those 

 to the south are from a highly cultivated country, practically 

 deforested. 



We may now consider the case of the Genesee and Oswego rivers, 

 referring to the large Geologic Map of the State of New York. 



Genesee river has an average rainfall of about 40 inches and 

 Oswego river of about 37 inches. That portion of Genesee river 

 which has been gaged lies almost entirely in the shales and sand- 

 stones of the Portage and Chemung groups. Oswego river, on the 

 contrary, lies in the horizon of the Portage sandstones and shales, 

 Hamilton shales, Onondaga and Helderberg limestones, Oriskany 

 sandstone, the rocks of the Salina or Salt group, the Lockport 

 limestone, Clinton limestone and shales, Medina sandstones, and 

 Utica sandstones and shales, including the Oswego sandstone. 

 The Chemung, Portage, and Hamilton formations have a wide 

 outcrop, while the Onondaga, Oriskany, and Helderberg are com- 



