PEORIAN INTERGLACIAL EPOCH. 303 



In the region under discussion the lowan drift has not been found outside 

 the Wisconsin, and nothing is known concerning the outUne of the lowan 

 drift border. The other hnes of evidence are, however, about as clearly 

 shown in this region as in that covered by the Illinois glacial lobe. A 

 comparison of the' weathering and erosion on the silt with that on the earliest 

 moraine and drift sheet of the Wisconsin series shows a perceptibly greater 

 change in the silt than has been effected in the surface of the Wisconsin 

 drift; but here, as in the Illinois lobe, the interval appears less prolonged 

 than the Sangamon interglacial stage. 



It was remarked in Monograph XXXVIII, in the discussion of this 

 interval, that the weathering appears to indicate that it is comparatively 

 brief, but that the change in the outline of the ice sheet and in the attitude 

 of the land may call for more time between the lowan and Wisconsin 

 stages of glaciation than the weathering seems to require. It should also 

 be remembered that the Toronto formation has fui'nished decisive evidence 

 of a prolonged interglacial interval.' Should it be proved to represent the 

 interval between the lowan and Wisconsin deposits its testimony should 

 outweigh any inferences of a brief interval drawn from a comparison of 

 the weathering of the two deposits. 



'See descriptions by Dr. A. P. Coleman and Prof. D. P. Penhallow: Am. Geologist, Vol. XIII, 

 1894, pp. 85-95; see also additional interpretation by Dr. Coleman: Jour. Geol., Vol. Ill, pp. 274, 

 622-645. 



