72 THE JOURNAL OF GEOLOGY. 



and disintegration would extend, would be dependent upon the 

 length of time during which the drift was exposed, and upon 

 the climate which affected the region during its exposure. The 

 longer the exposure and the warmer the climate, the deeper would 

 the weathering extend. If, subsequently, the ice .extended 

 over the same region, it might, in some places, override and 

 bury the old surface without destroying it. The earlier oxidized 

 and leached drift would thus come to be buried by the newer, un- 

 oxidized, unleached drift. If, therefore, beneath the newer drift 

 of any given locality there be found a lower drift, the surface of 

 which is oxidized and leached to a considerable depth, the evi- 

 dence is strong that the lower drift was exposed for a long period 

 of time before the upper drift was deposited upon it. Within 

 certain limits a similar result might be brought about, it is true, 

 if the ice, after having reached a certain maximum stage of ad- 

 vance, were to retreat for a short distance only and there remain 

 for a very long period of time. A subsequent minor advance 

 might bury the oxidized surface of the drift beyond the posi- 

 tion of the long ice -halt. Under these conditions, the climate 

 which would have obtained in the area of the drift exposed during 

 the minor retreat would have been cold, and oxidation, leaching, 

 and disintegration would have proceeded slowly. If they reached 

 considerable depths, the time involved must have been very 

 long. If this surface of oxidized and leached and disintegrated 

 drift were found to reach far to the northward beneath the layer 

 of newer and upper drift, it would indicate a great recession of 

 the ice. We maintain that if it were found sufficiently far north 

 of the margin of the overlying drift, and if its depth were suffi- 

 ciently great, extending well down below any possible accumula- 

 tion of superglacial till, it might be a positive criterion of so great 

 a recession of the ice, protracted through so great an interval 

 of time, as to constitute its new advance a separate ice epoch. 



There is much reason to believe that the soil developed 

 under the influence of a warm climate differs in some respects 

 from one developed from similar material under other conditions. 

 The well-known fact that red and reddish soils are especially 



