Chautauqua Grape Belt. 153 



■established. One of these last two outlets was past Chicago ; but 

 we know too little about the subject to state which one represents 

 this stage, or to tell where the third outlet was. 



At last the ice retreated far enough for the Erie basin to take its 

 present outflow past Buffalo ; but the valley of the St. Lawrence 

 was still ice dammed, and Ontario w^as raised to the level of the 

 overflow of the Mohawk valley. Thus temporarily the several 

 Great Lakes had their level raised by ice dams ; and during this time 

 distinct shore lines were formed. 



There are some differences from the present shore lines still to 

 be accounted for. Why, for instance, are there no rock cliffs, but 

 everywhere a series of beach gravels, a condition of so much import- 

 ance to the grape grower? It would have been a serious disadvan- 

 tage to have had the vineyards traversed by two or three rock 

 escai'pments like that of the present lake shore. In the first place, 

 the question whether the waves and currents shall cut or build 

 depends upon whether they are able to remove all of the material 

 that they obtain by one cause or another. That is the reason why 

 beaches are not built on some of the exposed head lands of the lake, 

 while they are commonly present in the enclosed bays, and why the 

 gravel accumulations opposite the mouths of the streams are more 

 extensive than elsewhere. 



There are various reasons why the waters of the ancient lake were 

 less able to remove the materials furnished them than is the case with 

 the present lake- As the ice was leaving the land, there was at first a 

 time when no vegetation covered the clay soil, and when the whole 

 surface was attacked by the rain just as a plowed field is to-day. 

 Therefore the streams were given more materials to carry to the 

 lake. In the second place, the rains must also have been heavier 

 when the cold ice wall was melting and furnishing vapor to the air. 

 Besides this, the streams entered the lake at the base of the hill, 

 while now they flow for a mile or two over a- plain. Another 

 important reason is the fact that the shores were gradually rising. 

 Therefore, for various reasons, the lake was given more materials 

 than the waves and currents could dispose [of, and hence they 

 accumulated in the gravel ridges which we find. 



A second important difference between the old shores and the 

 present ones, is the fact that they are no longer horizontal. This is 



