216 



PALEOZOIC TIME. 



by the close of the Lower Silurian ; but it still opened into a broad 

 oceanic basin near the longitude of Quebec; for both Upper Silurian 

 and Devonian strata, as has been stated, were formed over eastern 

 Canada and part of New England. 



6. Time of the Epoch of Disturbance This epoch is proved to 



have been between the Lower and Upper Silurian eras, as Logan first 

 observed, by the fact that unaltered and unconformable Upper Silu- 

 rian formations overlie in some places the upturned Lower Silurian 

 beds; as near Gaspe, on the Bay of St. Lawrence; near Montreal, on 

 St. Helen's Island and Beloeil Mountain ; at Becraft's Mountain, near 

 Hudson, west of the Hudson River ; in each of which cases the Lower 

 Helderberg beds overlie unconformably Lower Silurian slates; and 

 near Lake Memphremagog, where the Niagara limestone occurs with 

 its characteristic fossils, and also beds of Devonian corals. Again, on 

 the eastern side of the mountains, in the Connecticut valley, there are 

 unconformable Lower or Upper Helderberg beds at Bernardston, 

 Mass., and Littleton, N. H., which are evidence that the region ex- 

 tended here to the Connecticut. The earlier formations of the Upper 

 Silurian are scarcely represented, or are very thin, in the eastern part 

 of New York State, and this is apparently owing to the previous ele- 

 vation of the Green Mountain region. 



7. Somo Characteristics of the Force engaged The cause of the 



extensive uplifts and flexures of the Lower Silurian rocks had the fol- 

 lowing characteristics : — 



1. The force acted at right angles to the course of the flexures. — It 

 is obvious, without explanation, that only force from this direction 

 could have produced the result. 



2. The force acted from the direction of the ocean. — For the effects 

 are most intense to the eastward ; they diminish toward the interior. 



3. TJie force was slow in action and long continued. — This is evi- 

 dent from the regularity which the stratification now presents, not- 

 withstanding the upturning; for there is no chaos: the beds remain in 

 their old order, only bent into arches and bold flexures. The brittle 

 rock experienced the force so gradually that it yielded with little frac- 

 ture, except in the neighborhood of the axes of the folds, where the 

 strain was greatest. 



While all this upturning and crystallizing of strata was going for- 

 ward in western New England, and displacements to the eastward even 

 at Gaspe, there was comparative quiet north of Gaspe in the St. Law- 

 rence Gulf; for the great limestone formation of Anticosti, which was 

 begun in the Lower Silurian, continued its unbroken progress through 

 the whole prolonged era of revolution, and afterward far into the 

 Upper Silurian era. 



