88 A NATURALIST IN THE GREAT LAKES REGION 



north outlet, a natural embankment later used by railroads 

 entering Chicago from the east. The Desplaines no longer 

 emptied into the lake but was flowing south through the channel 

 of the old outlet. Below the main ToUeston beach are one or 

 two others showing apparently considerable fluctuation at this 

 stage. It is thought that Lake Chicago had become a part of 

 the greater Lake Algonquin, which included Lakes Superior, 

 Michigan, Huron, and more (Fig. 52). It was discharging 

 through Lake Erie. Probably some of these Tolleston beaches 

 were the shore lines of this greater lake. There is evidence that 

 the level of the water in the lakes dropped considerably below 

 its present level when for awhile the great lakes discharged 

 through Georgian Bay, the river Trent across Ontario to an 

 arm of the sea in northern New York (Champlain Sea) (Fig. 

 52). But finally through a gradual rise in these northern areas 

 the level of the water rose to the present grade, and the discharge 

 through Lakes Huron and Erie was resumed. 



It is interesting to note how human affairs are determined 

 by events that transpired hundreds of thousands of years ago, 

 long before man had even appeared on the earth. The route 

 followed by two great transcontinental railroads in entering 

 Chicago — the Chicago & Alton Railroad and the Atchison, 

 Topeka & Santa Fe Railway — is that of the old outlet of Lake 

 Chicago, and its location was determined by the presence of 

 the preglacial valley whose position w^as fixed by the lay of the 

 rock strata deposited in Paleozoic time. The same thing is 

 true elsewhere. The Lackawanna and the New York Central, 

 in leaving New York City for the West, follow the valleys of 

 old rivers that carried the main outwash from the glacier, and 

 their location was fixed by the lay of rock strata that were 

 deposited aeons ago. Lake Michigan, Desplaines River, and 

 the Illinois River were made a great north and south artery of 

 travel when the old preglacial valley continued past the present 

 site of Chicago down what later became the Illinois Valley. And 

 when the Valparaiso Moraine happened to so deposit that the 



