MICHIGAN ACADEMY OF SCIENCE. 
and the rocks are just such in lower Michigan, only well seen at such points 
on the edges of the peninsula, for here too they lie flat in great leaves or 
sheets. But across the North Sea in Europe or across Lake Huron and North 
Bay in our Lake region we come to another type of scene, so like in both 
cases that nothing in external nature tells us whether we are in the old world 
or the new. Hummocky tumbled granites in knobs and round waves of 
rock descend steadily if unevenly from the land beneath the sea. Seaward 
the knobs are all but submerged, a fringe of countless islands all of whose 
contours are round and smooth but of curves that are of short radius and con- 
stantly interrupt each other, intensely rugged, but the ruggedness is one from 
which all minor roughness and sharpness has been removed by some polish- 
ing agency. Naked toward the sea the shoreward face of brown islet and 
peninsula is scantily clad with plants. These resemblances across the At- 
lantic rest on a broader similarity in the structure of the continent. 
Glance for a moment on our map at the great chain of hollows between 
the mouths of the Mackenzie and the St. Lawrence, the great Canadian 
Lakes, as the old world calls them, including Great Bear, Great Slave, Atha- 
basca, Reindeer and Winnipeg as well as the five that we regard as ours. 
They lie along a four thousand mile curve encircling Hudson Bay. Broadly 
speaking the rocks north of this line are all ancient, crumpled, fireworn, 
Archaean rocks. South of the lakes the same lie deep beneath the flat layers 
of Paleozoics. It is on these flat lying rocks that most of the American 
people live. These are the great flat sheets of rock whose edges were said 
to crop out at Petoskey, at the tip of the Thumb and in the islands of Lake 
Erie. Among them are the Carboniferous rocks that carry our coal beds. 
In Europe a similar line of depressions may be followed through North 
Sea, Baltic, Gulf of Finland, Lakes Ladoga and Onega and the White Sea, 
under water most of it here, it stands so low. Here again for a rough des- 
cription we may say that the rocks to the north are all the ancient gnarled 
Archaean; to the south appear the flat lying layers on which live the mass of 
Europe’s people, English, French, German and Russian. It was a sample 
of this that we saw in the Orkneys and northern Scotland. 
These contrasts in the land nature are fairly well followed by the tree 
sorts on the two regions, to the north, needle-bearing conifers, to the south, 
broad-leaved, deciduous trees, though there are numerous excursions of either 
sort across the boundary, as for instance the pines on the Paleozoics of the 
southern peninsula of Michigan. 
The Baltic Shield of Archaean as has been said displays a type of land 
form strongly hinted at in the Archaean V south of Hudson Bay. The 
northern rocks in both cases are fused, molten, crystalline and hard, those 
of the south dull, earthy, layered and soft. Millions of years of weather 
had rotted and softened both kinds till their surfaces lav deeply buried in 
the resultant soils when another and singular thing befell. Its effects were 
much like the dragging of innumerable brush harrows southward across 
the Archaean areas and over the border of the southern cover layers. 
Details belong to geology. It is the story of the Ice Age. The process 
swept off the decayed and softened surface portions of the Archaean rock, 
baring firm, sound, unweathered rock below, which is smoothed and polished 
at the same time that it left it hummocky and nubbly as its gnarled and 
crumpled structure demanded. As the sweeping process did not extend far 
into the southern areas their rocks were rarely stripped, but rather received 
the sweepings from the north upon their own soils. Thus it happens that 
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