20 ABSTRACT OF VOLUME. 



have suffered a much greater amount of erosion and weathering than the Illinoian 

 drift. Its characteristics are set forth, and the glacial drainage connected with it is 

 discussed. 



Chapter VI. The Illinoian drift. — This embraces the portion of the Illinoiaa 

 drift exposed outside the Wisconsin drift from the reentrant angle in the glacial 

 boundary in southern Indiana eastward to central Ohio, where its border passes 

 beneath the Wisconsin drift border. Its structure and topographic expression and 

 the character of the glacial drainage are discussed. 



Chapter VII. The Sangamon soil and weathered zone. — The weathered 

 zone and accompanying soils and peat beds which occur between the Illinoian drift 

 and the overlying loess are described in their exposures outside the Wisconsin drift, 

 and to some extent within the limits of that drift. 



Chapter VIII. The loess and associated silts. — The lowan drift does not 

 appear to be exposed in this region outside the Wisconsin drift, but a deposit of silt 

 of loess-like characteristics occupies the horizon of this drift sheet. It maj^ be to 

 some extent a dependency of the lowan drift, for the loess in the vicinity of the 

 Mississippi River is found to have that relation, as indicated in Monograph XXXVIII. 

 The mode of deposition is, however, considered problematical. 



Chapter IX. The Peorian or post-loessial soil and weathered zone. — 

 The evidence of this interval between the loess deposition and the Wisconsin gla- 

 ciation is found in the relative amounts of weathering displayed by the loess and the 

 Wisconsin drift. It may also be inferred from the change in the attitude of the 

 land by which better drainage conditions became prevalent in the Wisconsin than 

 obtained in the lowan stage of giaciation. The marked difference in the outline of 

 the lowan and Wisconsin borders also indicates an interval of some consequence. 



Chapter X. The early AVisconsin drift. — The early Wisconsin drift is less 

 extensively exposed in this region than in that covered by the Illinois glacial lobe, 

 discussed in Monograph XXXVIII, there being in southwestern Ohio but one 

 moraine and a narrow till plain which seem referable to this drift, while in central 

 and eastern Ohio and northwestern Pennsylvania it has a still more limited exposure. 

 In southeastern Indiana two moraines of the White River lobe and one of the Miami 

 lobe seem referable to this drift. The present I'eport embraces only the part of this 

 drift extending from the Miami lobe eastward. It treats of both the drift and the 

 outwash connected with it. 



Chapter XL The interval between the early and late Wisconsin 

 DRIFT. — The evidence of this interval is more clearly shown in the region covered 

 by the Illinois glacial lobe than in this region, for there the border of the outer 

 moraine of the late Wisconsin group is strikingly discordant with that of the neigh- 

 boring moraine or moraines of the earlj^ Wisconsin group, while in this region there 

 is not a marked discordance. There is, however, in this region, as well as in the 

 Illinois region, a marked contrast in the topography of the moraines, those of the 

 earl}^ Wisconsin having smooth ridges without lakes or deep basins on them, while 



