332 F. Carney — Wave-cut Terraces in Keiika Y alley. 



however, is attached to this vertical position, further than to 

 note that it could have no genetic association with the bench. 

 The original relationship of terrace and cliff, so far as analysis 

 of a particular cross-section is concerned, has been given much 

 indefiniteness by the agents of degradation ; whereas this rela- 

 tionship is still conspicuous when viewed from a distance. 



As a distinct feature of the slope, this terrace disappears 

 where the valley wall becomes very steep towards the southern 

 end of the Bluff. The till at the end of the Bluff is made up 

 largely of local material; there is other evidence also of vigor- 

 ous corrasive work bv the glacier on the slopes near the end of 

 Bluff Point. 



No. 3. On the supposition that these terraces represent a 

 body of water that fell successively to the levels indicated, 

 terrace No. 3 is the oldest ; but the difference in the degree of 

 weathering attained, or in the sharpness of profile, is not 

 noticeable. This terrace apparently does not extend as far 

 north as No. 2; there is, however, some obscurity in this direc- 

 tion due to its disappearing beneath a wide band of drift. 

 Furthermore its identification is not obvious quite as far south 

 as Ogoyago ; so terrace No. 3, in linear extent, falls short of 

 the next lower terrace. 



Thne Periods of these Cliffs. 



The measure of post-Pleistocene time has been attempted 

 through several lines of observations : The years involved in 

 the carving of the Niagara and other gorges, in the construc- 

 tion of flood plains, etc., have been estimated relatively to 

 units which do not admit of very accurate determination 

 because of the interdependence of degradational activities, a 

 variation in any one of which would give the units quite dif- 

 ferent values. Time-ratios of the continuity of certain phases 

 of geological activities are less objectionable. 



From a study of the extent to which erosion has effected the 

 several sheets of till, certain ratios have been deduced using 

 the erosion period of the Late Wisconsin drift as a time-datum. 

 The approximate value of this ratio, which may be subject to 

 alteration through the acquirement of new facts, for the Early 

 Wisconsin is 2 ; for the Iowan, 4 ; for the Illinoian, 8 ; for the 

 Kausan, 16.* The drift of the Mississippi Basin has furnished 

 most of the data concerning these epochs of glaciation. It 

 has already been established that the glacial period in the East 



* Charnberlin and Salisbury, Geology, vol. iii, pp. 413-421, 1906. Here is 

 found a succinct pi*esentation of the data on which are based the relative 

 time-periods of the stages of the Glacial Period. 



