Page Eight 



EVOLUTION 



January, 1938 



foreign rock must have been brought here in some way 

 from some place which has a granite bedrock. 



Now, what's the next step in our reasoning? You will 

 probably beat me to the idea before I can announce it. 

 If the granite and other foreign rock fragments were 

 brought to the Chicago region, and if in the bringing, they 

 were scratched and the bedrock limestone here was scratched 

 and fluted in a northeast-southwest direction, then the 

 granite, etc., came from the northeast or the southwest. 

 That it came from the northeast is clear when we find that 

 there are fragments here from the outcropping bedrock 

 north of Lake Superior and Lake Huron. Even pieces of 

 the native copper of the Lake Superior copper country are 

 found now and then. 



The Clay Was Left by Glaciers 



But what brought the foreign boulders and stones from 

 the northeast } What forced them to gouge and plane and 

 smooth the underlying limestone? What ground up the 

 softer material to make the clay ? The geological agencies 

 which shift materials about on the earths surface, and 

 which wear the material in transit, are waves, streams, 

 wind and glaciers. Waves never move, or deposit, such 

 heterogeneous material as clay and stones together, and 

 they never mark the bedrock m the tashion we saw in the 

 clay pit. Streams are likewise guiltless. Wind never did 

 anything of this sort, though, admittedly, the wind does 

 blow sometimes in Chicago. But the glaciers of our western 

 mouncains and ot Alaska and of Greenland and ol Ant- 

 arctica make precisely similar deposits and mark their debris 

 and the bedrock over which they move, in precisely the 

 same manner. 



So here at last we reach a conclusion that seems perfectly 

 logical and in perfect accord with the facts. We have used 

 the scientific inductive method in solving the problem. We 

 have no alternative explanation except that "the clay was 

 here in the first place" — and that's no explanation. 



Now that we have proved that the Chicago region has 

 been covered by an ice sheet, you may lay down that brick ! 

 We are going farther afield. We scout about Wisconsin, 

 Illinois, Indiana, Michigan and adjacent states. Every- 

 where we find the same typical glacial record. Wait ! We 

 fail to find it in southern Illinois, southern Missouri, south- 

 ern Indiana. We soon find that we can draw a line across 

 the United States, from east to west, north of which is the 

 record of glaciation, and south of which none of this 

 record can be found. The ice-sheet spread from the north- 

 ern part of the continent down into New Jersey, Penn- 

 sylvania, Ohio, in one place about 20 miles over into Ken- 



The Far Flung Front of the Ice Sheet 



tucky, Indiana, Illinois as far south as Carbondale, Missouri, 

 northeastern Kansas, eastern Nebraska and eastern South 

 Dakota, most of North Dakota, northern Montana, Idalio 

 and Washington. All Canadian territory was under the 

 great ice-sheet. Indeed, the ice-sheet was a Canadian prod- 

 uct for it centered near Hudson Bay and spread out in all 

 directions. Yes, it actually moved northward from the 

 continent toward the Arctic Sea. 



The Ice Sheet Made Our Lakes 



The influence of that ice-sheet today is manifold. Almost 

 all of the hills and valleys of the northern states which I 

 have named are the result ot that glacial experience. Rarely 

 do we find a region where the bed rock makes up the hills. 

 Most of them were built up by the deposits made by the ice. 

 The ice was a gigantic rasp, thousands ot teet thick, armed 

 below with fragments of rock picked up in its course, and 

 this wreaked havoc with the pre-existing hills and valleys 

 of the invaded region. Then, when the ice melted (tor 

 that is the only way it could be removed) all the detritus 

 worn and torn ott the underlying rock from Labrador 

 southward, was left behind, resting on the planed and 

 smoothed and scratched bed rock floor. (We're back to 

 the clay pit, again, you see.) 



The old river valleys in many places were completely 

 filled and the streams had to find new courses. Niagara 

 River is the most spectacular case of this sort. The new 

 course just happened to cross a cliff of limestone and the 

 balls of Niagara resulted. 



The multitude of lakes ot northern Michigan, northern 

 Wisconsin and northern Minnesota all owe their existence 

 to the irregular deposition of the glacial debris. How many 

 of the honeymooners at Niagara and how many of the 

 fishermen in the lake country appreciate this ? Oh, well — 

 you can't blame them! Love and fish are matters of vital 

 moment — glaciers are not. 



Almost all the soils of the northern states are due to 

 the glaciation. The glacial deposits have been worked over 

 somewhat at the surface, rain has percolated thru and dis- 

 solved some substances, organic matter has been added from 

 the prairie sod or the forest duff ; otherwise we are farming 

 on the ground-up debris left by the ancient ice sheet which 

 covered nearly half of North America. 



Most interesting, perhaps, is the fact that our Great 

 Lakes owe their existence to the glaciation. Before the ice 

 invaded from the north, these lake basins were simply 

 broad river valleys. The ice sheet was thousands of feet 

 thick, its surface, if like that of the Greenland and Ant- 

 arctic ice sheets of today, was fairly level, but its bottom 

 fitted down to the major pre-glacial hills and valleys. It 

 therefore was thicker where the valleys were, and there it 

 eroded more. Then, during the waning of the glaciation, 

 it lingered longer in these lower places and built up the 

 southern margins of the basins to make the dams which 

 today withhold the lakes from flowing to the Mississippi. 

 New outlets were found, converging to the St. Lawrence. 

 Niagara, as I have indicated, was one of these post-glacial 

 outlets. 



(To be continued in next issue) 



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