INDUSTRIAL GEOLOGY. 149 



closely study these ice rivers, the mighty glaciers, and can actually witness 

 their wrenching the rocks asunder, grinding the hardest rocks to very powder, 

 plowing up the rock surface as though it were a mellow soil, and tlien freezing 

 on to the ground and broken fragments and bearing tliem on for miles and 

 dropp ng them as the glaciers melt and so lose their grip. In Greenland the 

 glaciers move down the island and pass into the ocean, and thus arise the tre- 

 mendous icebergs whicli are the dread of the mariner even as far south as our 

 own latitude. These icebergs, as they melt, drop their load of Greenland soil, 

 and thus are constantly forming the banks off Newfoundhind, where so many a 

 vessel has been wrecked becau-e of these same treacherous rocks ; seemingly 

 angry that their own voyage is over, tiiey seek vengeance upon other voyagers. 

 Prof. Agassiz was the first to show that our whole northern latitudes had once 

 been ground, plowed and graded by these same mighty ice rivers. Our own 

 State shows in the yet lingering furrows, in the Inige banks of boulder clay, and 

 in the widely scattered hard heads, not one of which hal its birthplace this side 

 of the Upper Peninsula, that it was once overspread, plowed and harrowed by 

 these mighty ice plows. Thus we see liow nature tilled her soil and prepared it 

 for man's use. These glaciers passed as far south as the Ohio river, and as they 

 melted the ground and broken rock which they held in their grasp was Avashed 

 along and stranded on the more southern and Gulf States. Michigan, then, 

 has been subjected to the erosive force of both the agents mentioned. The old 

 glaciers acted as the great breaking up and sub-soiling plow which, driven by 

 nature, plowed deep and well. Since the glacial era, running water has been 

 the harrow which has leveled and mellowed, till our State became a very garden 

 spot, which was so well demonstrated by tlie mighty forest which she grew. 

 This glacier era did not occur till very near our own time ; not till towards the 

 close of the recent life time. You will remember that Michigan was completed 

 or raised above the ocean level at the close of the ancient life time. Thus we 

 may say that Michigan was a great fallow, or more properly that she was in 

 permanent pasture for ages. Daring all this time she was growing richer and 

 richer, for nature in her tillage never sells either coarse or fine crops off the 

 farm. Thus before the eastern border, the Southern and Gulf States, and the 

 great west were in existence, Michigan was the seat of rich herbage and grand 

 forests. 



We have already noted how the successive rock areas from oldest to later date 

 in the old life time were deposited and raised above the ocean level from North 

 to South in our Michigan region ; we have also seen how these rocks would 

 vary. Some would be sand, some shale, otheis lime, according as the water 

 during their formation was shallow, deeper, or quite deep. In these successive 

 rock areas in Michigan, sonie, like the Pictured rocks, were mainly sand rock ; 

 others were as peculiarly shale, and still others lime. We may say then that 

 the old rock floor of Michigan was a sort of mosaic, the separate blocks of 

 which were as various as are the rock materials of the earth's crust. AVe see 

 then that the old glaciers, as they came to load up their huge dirt wagons, had 

 all kinds of rock to shovel, and more had a surface soil to load on that had 

 been enriched by the accumulated deposits of ages upon ages of rich vegetable 

 growths, which had been increasing under the stimulating influence of its own 

 death and decay. We all know that our best soils are most varied in their 

 composition, are well ground up and mellowed, and are well enriched by the 

 accumulated deposits of long ages of growth and decay. Thus we see that our 

 own Michigan in its very geologic history, from the varied rocks which yielded 

 its seed bed from the long ages— all the years of middle and recent geological 



