LOESS IN THE WISCONSIN DRIFT FORMATION 93 I 



glacial epoch, but also because its relations show, in at least one 

 of the two localities, that it is not the work of wind. 



Super-till loam about Green Lake. — ^All about Green Lake it is 

 a striking fact that the till, and indeed the drift in general, is 

 covered by a layer of loam two to five feet thick, which is suf- 

 ficiently different from the underlying drift to attract attention. 

 It varies from a moderately stiff clay on the one hand, to a 

 rather sandy loam on the other. It is generally heavier than 

 its substratum, though influenced to some extent by it. Where 

 it overlies stratified drift, it is on the whole less clayey than 

 where it overlies till. It is sometimes altogether free from 

 stony material, though this is not the rule. The absence of 

 ston}' material is more likely to be the fact where the loam is 

 thick than where it is thin, and where it overlies stratified drift, 

 than where it overlies unstratified. The stony content of the 

 loam may be either coarse or fine. If it contain bowlders, as it 

 sometimes does, they are in all cases, so far as seen, of a some- 

 what distant origin. Among the drift bowlders of the region 

 diabase predominates, and every bowlder seen in the loam was 

 of this type. The bowlders of the loam do not differ in shape 

 from the bowlders of the same sort in the body of the drift. 

 On the other hand, where the loam contains small stones they 

 are in almost all cases of chert such as might have come from 

 the local rock, especially the Lower Magnesian limestone ; but 

 in small bits it is not always possible to distinguish Lower 

 Magnesian limestone chert from chert of other formations. 

 The cherts are almost uniformly sharply angular. The stony 

 matter both of the bowlder type and of the smaller pieces is 

 more likely to occur at or near the base of the loam, than at or 

 near its top. Occasionally there is an aggregation of small 

 stones at the junction of the till and loam. So well developed 

 and so persistent is this loam that the surface of whole fields 

 and even farms is without a trace of bowlders, even where the 

 till is notably bowldery. 



There seems to be no special rule concerning the topographic 

 distribution of the loam, further than that it is generally most 



