224 matured /ifciracles, 



to its present dimensions, while the glacial 

 drift was deposited at what is now the head of 

 the lake, filling up the old outlet and thus 

 making a great dam. The damming up of 

 these great water courses was another cause 

 for increasing the width of these lakes. In a 

 similar way Lake Erie was formed. It is sup- 

 posed, however, that this lake is entirely the 

 product of glacial action, as there is no evi- 

 dence of an old river bed in its bottom; be- 

 sides, it is much shallower than the other 

 lakes. The same action that formed Lake 

 Erie filled up the old river bed running 

 through the province of Ontario, so that when 

 the ice receded Lake Erie became the new 

 channel for the old river. The same process 

 filled up the Valley of the Mohawk to more 

 than 100 feet in depth and also raised the 

 Valley of the Hudson. This caused the new 

 channel to be made through the Niagara Eiver 

 and a new route to the ocean for the drainage 

 of all the chain of lakes through the St. Law- 

 rence. It will be seen that the bottoms of all 

 of these great lakes to a certain extent were 

 worn out by the action of running water, ex- 

 cept Erie. The great glaciers widened them 

 out, and in the case of Lake Erie scooped it 

 out. At the same time it built great dams 

 across the outlets which raised the surface of 

 the water to a much higher level and caused 

 them to form new outlets, thus changing the 



