178 T. C. Charriberlin — Diversity of the Glacial Period. 



agencies, it seems to me probable that the region will prove to 

 have been largely, possibly completely, covered by ice in the 

 earliest stage of the second glacial epoch. It is not, however, 

 traversed by conspicuous moraines, at least not by any as well 

 developed as those above outlined. Low ridged belts of sub- 

 dued morainic aspect have been observed at numerous points, 

 but their relations have not yet been traced out. 



"A similar qualifying remark may be here made concern- 

 ing a considerable area in Northern Illinois, outside the mo- 

 raine described in this paper. The freshness of its drift, and 

 the unsculptured contour of its surface, bear evidence of 

 recent origin. Some portions of this area seem clearly to be 

 of lacustrine and fluviatile origin, at least supernciallj', and I 

 have at times supposed that all might be due to waters mar- 

 ginal to the adjacent glacier, since there is no conspicuous 

 bordering morainic ridge ; but the tendency of recent evi- 

 dence, gathered in a 'special study of this class of deposits, 

 seems to favor the hypothesis of more extensive glacial occu- 

 pancy, even where the evidence of it in obvious moraines is 

 feeble or wanting. This questionable region is now under 

 investigation. The dotted lines on the map indicate some of 

 my working hypotheses." 



Prof. Wright neglects to say that my later mapping relates 

 to this area, thus announced to be under investigation, and 

 that its morainic lines were such as the preliminary map had 

 foreshadowed. He further failed to say that this later map 

 was one constructed merely to exhibit the location and direc- 

 tion of strise in connection with my paper on "Rock Scorings 

 of the Great Ice Invasions."* I have not yet re-discussed the 

 region nor the moraines in question. The more recent investi- 

 gations bring out into clearer definition and justification the 

 ground of doubt which lay in my mind at the time of the 

 first mapping, for they show that there are two groups of 

 moraines representing two important episodes of glacial his- 

 tory, and that both mappings will be retained, when corrected 

 and perfected, as factors in an ultimate differential map of the 

 drift of the region. To demonstrate their exact correlations 

 east and west still remains difficult, because the later lines 

 override the earlier at large angles and conceal their connec- 

 tions, and because the moraines of both epochs bunch them- 

 selves in the reentrant angles between the ice lobes in such a 

 way as to make their demonstrative disentanglement a work 

 of extreme difficulty. On this account I have left the pro- 

 visional correlations set forth in the earlier paper standing 

 without re-discussion, that the work of later correlation might 

 be the freer. 



*7th Ann. Rep. U. S. Geological Survey, pp. 147-248. 



