58 F. B. TAYLOR — CORRELATION OF BEACHES AND MORIANES. 



ously the great dam that held all these waters up. This has been the 

 theory of the leading geologists of America for many years ; but those 

 who have opposed the idea of the continental ice-sheet on general princi- 

 ples have always had some advantage in being able to assert that the 

 exact place of the dam had not been discovered in any important case. 

 They have demanded some evidence of the existence and exact place of 

 the ice-dam that held up lake Iroquois, and the same for lake Agassiz, 

 and such evidence has not been found ; but in both of these cases there 

 are great difficulties in the way of locating the ice-dam with precision. 

 In both regions the country is rough, and moraines are hard to trace, 

 while for lake Agassiz the country is also almost wholly inaccessible. 



In Michigan neither of these difficulties was encountered. The re- 

 gion is generally so smooth that the moraines and outlet channels them- 

 selves constitute the main reliefs of secondary magnitude, and most of 

 the country is well cleared. While it is true that for each stage of the 

 waters described above something yet remains to be done before its 

 exact boundaries can be fully known, it is nevertheless true, in the 

 opinion of the writer, that the position of the ice-dam for all the lakes 

 here described is either known exactly, as in the case of lake Maumee 

 and the western end of lake Whittlesey, or is reduced to a narrow choice 

 of alternatives. What now remains to be done to complete our knowl- 

 edge of all these boundaries is a small thing compared*with what has 

 been accomplished in this direction in the past. 



The writer takes pleasure in acknowledging helpful suggestions in the 

 interpretation of some of the facts from Mr Gilbert and Mr Leverett. 



