INTRODUCTION. 29 



only one prominent morainic system (the Valparaiso) while the Huron-Erie ice border was 

 receding across Indiana and Ohio about to the limits of the Erie basin and developing several 

 moraines in the course of its retreat. It would seem more natural for the two parts of the 

 Labrador ice field to have had a similar mode of recession instead of this discordance, and it 

 now seems likely that the features noted are such as might be developed where ice currents 

 from different directions were meeting on common ground, but where neither dominated strongly 

 over the other or persisted after the other had withdrawn or melted away. 



The bowlder belt, though reaching 5 to 10 miles beyond the line of junction marked by the 

 eastern termini of the ridges of the Bloomington morainic system makes really a very slight 

 overlap in comparison with the .great area of the two divisions of the Labrador ice field, and 

 there seems no great difficulty in explaining it -on the basis of slight encroachment of the eastern 

 movement into territory which had been occupied by the Lake Michigan glacier. This over- 

 lapping may perhaps have been merely in the surface portion of the ice sheet, and thus may 

 not have affected the basal portion. The bowlder deposition may have begun at the south at 

 the time when the oldest of the four moraines of the Bloomington system was forming and 

 have extended northward with the recession of the ice border along the junction of the Lake 

 Michigan and Huron-Erie ice and not have been completed until the last of the ridges of the 

 Bloomington system had been formed. In other words, the bowlder belt would mark a line 

 of recession instead of the trend of an ice border. 



After the development of the Bloomington morainic system there seems to have been 

 rapid recession along the junction of the Lake Michigan and Huron-Erie lobes across the Kan- 

 kakee basin and on northeastward into southern Michigan as far as the Kalamazoo Valley 

 east of the city of Kalamazoo. Along this line are numerous bowldery patches and morainic 

 areas that appear to pertain to an interlobate moraine, and extensive outwash aprons that 

 make it possible to work out in a rude way the progress of the recession. 



As the terms earher and later Wisconsin were introduced under the view that there had 

 been a great shifting and readjustment of the ice currents the present distrust of the correct- 

 ness of that view necessitates the suspension of the use of the terms so long as the distrust 

 continues. It may be necessary to revive the terms if further investigation discloses a clearly 

 defined basis. It is probable that the outer moraine of the Green Bay lobe and, indeed 

 much of the Wisconsin border in Wisconsin, Minnesota, Iowa, and the Dakotas may be 

 younger than the Shelbyville morainic system of the Illinois lobe. If such should prove to be 

 the case, it might be convenient to refer to the older portion of the Wisconsin border as earlier 

 Wisconsin and to the younger portion as later Wisconsin. This matter, however, is not 

 important in the area covered by the present monograph and may be left with this passing 

 suggestion. 



Attention was directed in Monograph XLI (pp. 352-353) to certain broad, shallow valleys 

 cut in outwash gravels of the earher part of the Wisconsin stage in the reentrants between 

 the East White and Miami lobes and the Miami and Scioto lobes. The morainic ridges of the 

 main system cross the beds of these channels in such way as to show that they were later than 

 the channeling. The cuts are shallow, being generally only 25 to 50 feet deep, but in places 

 reach a width of 2 miles or more. The amount of work done seemed to the writer at the 

 time Monograph XLI was written to require a considerable time, and it was referred to the 

 interval between the earlier and later Wisconsin drift. Subsequent studies in the southern 

 peninsula of Michigan, however, have brought to light other instances of large erosion in 

 reentrant angles between ice lobes or in places where glacial drainage was greatly concentrated, 

 and this erosion seems to have occurred hi the ordinary recession of the ice sheet without 

 the lapse of a long interval such as was postulated in eastern Indiana and western Ohio. The 

 writer is not at present disposed, therefore, to allow so much time as he formerly did for the 

 erosion of these channels, for in both of them there must have been great concentration of 

 glacial drainage. 



