366 Story of the Mississippi-Missouri .— Claypole. 
in the east save by means of their organic remains. The 
study of the fossils has been the only means of binding the 
two together where it was not possible to trace the beds con¬ 
tinuously from one place to the other. 
Although taken as a whole the palaeozoic era was, in the 
midland states, a quiet and undisturbed time yet there were 
not lacking signs of coming trouble. In the later portion of 
the Ordovician age, or perhaps in the early part of the 
Silurian, a thrust occurred which had the effect of bending 
the strata already deposited and of forming a long, low arch 
extending from the southwestern portion of Ontario near the 
southern end of the Georgian bay through Ohio and Kentucky 
into and beyond Tennessee. The flexure was slight but its re¬ 
sults were great on the geology of those states. 
At about the same time and owing probably to the same 
cause, whatever that may have been, a similar thrust elevated 
the Green Mountain region which has ever since remained 
above water. This change probably cut off the previously 
existing connection between the interior basin and the sea to 
its northeast. 
Again at the close of the Devonian age were heard the mut- 
terings of the restrained earth-forces. The strata laid down 
during all this period in Maine and in some other parts of the 
northeastern states and adjoining regions of Canada suffered 
compression and were folded, crushed and elevated above the 
sea-level. 
But the great catastrophe did not come till the end of the 
palaeozoic era. Then the long period of rest was broken by 
violent thrusts from the southeast before which the massive 
sediments gave way and were flexed and crushed as so many 
sheets of paper. The long arches of the Appalachians arose 
fold behind fold just where the strata were thickest. From 
these arches have since been carved by erosion the Allegheny 
mountains which despite their hight and extent are but the 
fragments of the thicker and heavier masses of strata out of 
which they were made. 
The “ Appalachian revolution ” as this great catastrophe in 
the geological history of North America has been aptly named, 
not only raised the vast rampart of the Allegheny mountains 
between the interior basin and the Atlantic ocean but it also ^ 
produced or at least was synchronous with the permanent dry- 
