BOTANY OF L,A SALLE COUNTY. 5 



furnish a fossil or two, there is no difficulty in tracing* 

 it to its source. It is unquestionably Niagara lime- 

 stone which has been broken up, the fragments some- 

 what rounded and smoothed and moved from some 

 other locality to the places where we now find it, for 

 when we bore a deep well in this region we find no 

 traces of the Niagara limestone, but we do find strata 

 that belong below it far below it. Hence we are led 

 to the conclusion that the Niagara never existed here. 

 But where did the hard, dark or light rocks, for they 

 are of many colors ,come from? The nearest point at 

 which we find any trace of them is about seventy-five 

 miles north of the south line of Wisconsin and for the 

 original home of others we must go to the south shore 

 of Lake Superior. But if they came from these distant 

 places how did they get here? We know of but two 

 methods. They might be rolled onward by waters or 

 borne from their native beds by ice in the form of 

 glaciers, and that the gravels were transposed by 

 water and the blocks by ice we think substantially 

 established. If we suppose the country about Hud- 

 son's Bay to be covered by ice several hundred feet 

 thich and remember that ice is as amenable to pressure 

 as wet clay, we can readily understand that the 

 weight of the superincumbent matter would tend to 

 force the ice, as it were, to flow out around the bottom 

 and that the greater the depth over the buried region 

 the greater the force causing the outflow and the far- 

 ther it would extend and this force might be so great 

 as to cause the ice to reach out in long streams as gla- 

 ciers and even sufficient to force it up and over consid- 

 able hills. It would of course flow through valleys 

 and low lands until these were all filled up. When 

 one of these streams encountered a ridg-e it would pile 

 up against it, slowly climb it and as it went down the 



