226 KANSAS ACADEMY OF SCIENCE. 



ceding epoch? If the front of the ice during any epoch should advance far- 

 ther than it did at the culmination of the last preceding epoch it would leave 

 enough of these rocks accompanied by other debris to form a distinct moraine, 

 possibly composed largely of rocks collected in the last few miles. Such 

 moraine would lose its morainic character after the lapse of a sufficiently 

 long time; and there would be nothing left but these hard rocks, ready to be 

 moved forward if need be at the culmination of the next succeeding epoch. 

 We may find out, approximately, perhaps, where any of these stones came 

 from originally; but can we tell how many times they rested for 20,000 years, 

 more or less, at a time, before they reached here? 



At the ordinary rate of travel of ice in a glacier, this piece of jasper 

 could easily have been moved from New Ulm, Minn., to Topeka, Kan., in a sin- 

 gle epoch; but, as this piece is unconnected with any quartzite, and as Prof. 

 U. S. Grant says that at New Ulm it forms pebbles in the base of the Sioux 

 quartzite, but is found in mass on both sides of Lake Superior, it is more 

 reasonable to suppose it came originally from north of Lake Superior, and 

 that it reached here by stages. 



TIME OF THE ICE EPOCH. 



If the height of the last platonic winter occurred say 11,350 years ago, and 

 the obliquity of the earth at that time was 30 degrees, it is easy to see that 

 there would be no great trouble in the ice being pushed from Hudson bay 

 down into southern Minnesota, even though the ellipticity of the earth's 

 orbit were no greater than at present. 



And whenever the greatest obliquity of the earth's axis coincided with the 

 greatest ellipticity of the earth's orbit, and both coincided with the earth 

 reaching its perihelion about the 4th of July, the greatest glacial epoch would 

 take place; and this was when the ice was pushed to its utmost extension in 

 Kansas, and was what Prof. T. C. Chamberlin calls in Geikie's Great Ice Age 

 the "Kansan" epoch, to indicate and individualize the epoch during which 

 the ice reached its greatest extent toward the south, and to individualize the 

 deposit made during that epoch, as is clearly shown in this boulder train 

 through Shawnee and other counties of Kansas. The number of platonic 

 years that have passed since then has not yet been accurately calculated; 

 neither has the number of ice periods, only approximately, and supposed to be 

 five; which would place the Kansan epoch, as this is the middle of the pla- 

 tonic summer in the northern hemisphere, between 110,000 and 125,000 years 

 ago. 



Further study will be given this subject. 



