87 



Post-Devonian Events. — We have now traced the history 

 of this region from the time of the Lower Devonian to near 

 the close of the Upper Devonian time, when it was raised 

 into drv land. The changes which were going on outside of 

 this area after its elevation, are out of place in this dis- 

 cussion. The interval which elapsed between the close of the 

 Devonion era and the beginning of the Quaternary era, can 

 be passed over briefly. It was a long interval, during which 

 the atmosphere, the rivers, and the sea exerted their com- 

 bined influences to destroy the new-formed land again. 

 Much of the material deposited in the Carbonic sea was 

 derived from the erosion of the land, which had been formed 

 in the age just preceding. 



It was during this interval of time that the slight crust- 

 movements occurred, which gave rise, on the one hand, to the 

 faults and folds, and on the other to the joint-cracks which 

 traverse these rocks. The beds which at first were horizontal, 

 or nearly so, were tilted until they stood at the present angle. 

 The lithification of the beds, probably commenced while they 

 were still submerged, continued, and ultimately, the shales 

 and sandstones as we see them to-day, were produced. 



At the end of this long period of erosion, we find some 

 interesting topographical features, which are no longer in 

 existence. A broad and deep river valley had been carved 

 out of the strata where Lake Erie is now. A stream— the 

 Idlewood River— coming from the south-east, entered this 

 valley through a gorge, half a mile north of the mouth of the 

 present Eighteen Mile Creek. Then came the great "Ice 

 Age," and all the country was buried beneath the accumu- 

 lating mantle of snow and ice. When, through its increased 

 thickness, and through melting at its southern end, this 

 great ice sheet began to move, it scratched and polished the 

 bed rocks, by means of the pebbles and sand frozen into its 

 under side." 



*The glacial history of this region is too intricate, and involves the detailed con- 

 sideration of regions" outside of those treated of in these chapters; therefore its 

 complete discussion will not be taken up in this paper. See Gilbert's History of 

 Niagara Falls, National Geographic Monographs, Vol. I., No. 7, and numerous 

 papers in various Journals referred to in the appendix. 



