586 SAMUEL CALVIN 



was laid down on an uneven surface; but at the point illustrated 

 in Fig. i, the section of the till, including the black loam at the 

 top, is about eight feet. That the later and newer till is uncon- 

 formable on the gravel is shown in Fig. 2. The typical bowlders 

 of the Iowan drift belong to this overlying till; there is nothing 

 corresponding to them in the blue Kansan. In the process of 

 excavation a number of the Iowan bowlders were undermined and 

 allowed to fall into the pit. One such, perched on the brink of 

 the excavation, is shown in Fig. 3, and a larger-sized companion, 

 completely undermined, has fallen in. The typical, young, un- 

 eroded, bowlder-dotted surface of the younger drift, which stretches 

 away from the margin of the old working, is illustrated in Fig. 4. 

 A quotation or two from the report on Buchanan County, Iowa 

 Geological Survey, VIII, may be pertinent. On pp. 239-40 we read: 



A very common relation of Pleistocene deposits is illustrated in the well 

 section on the land of J. W. Welch in the southwest quarter of Section 28, 

 Buffalo Township. The record shows: 



Feet 

 3. Dark soil and yellow till 4 



2. Reddish, ferruginous sand and gravel 23 



1. Blue clay, penetrated 1 



No. 3 of this section is Iowan drift, No. 2 is Buchanan gravel, and No. 1 

 is Kansan till. 1 In the same quarter section another well shows, 



Feet 



3. Soil and yellow till 22 



2. Reddish gravel 1 1 



1. Blue clay, with pockets of sand 19 



Although the thickness varies considerably, the members of this last 

 section are severally the same as the corresponding numbers of the one above. 



In another part of the same report, p. 209, it is recorded that 

 "the eastern part of Fairbank Township is a very level, dry plateau 

 in which a sheet of Iowan drift varying from two or three to thirty 

 feet in thickness overlies an extensive bed of Buchanan gravels. 

 The plateau is a unique piece of prairie land, without the usual 

 undulations, and without any indications of imperfect drainage. 

 The underlying gravel seems to afford an easy means of escape for 

 the surplus surface waters." 



1 Owing to an error in proofreading the terms Iowan and Kansan are transposed 

 on p. 240 of the volume cited. 



