216 PALEOZOIC TIME. 



was probably defined before tbe Silurian era began, by Archaean up- 

 lifts along the Green Mountain area ; but, if not, it dates from this 

 epoch, as suggested by Logan. It lies where unstable or oscillating 

 New England, through Lower Silurian time, hinged on to the stable 

 Archaean ; or, just where the heavy pressure during the era of disturb- 

 ance operated against the stable Archaean, as it folded up the thick 

 series of rocks to their bottom. 



Moreover, the great St. Lawrence gulf about Ottawa, where the 

 Trenton and Cincinnati formations had been accumulated, was prob- 

 ably nearly obliterated at this time ; for no rocks of more recent date 

 occur there, to prove the presence of the sea, until the Quaternary 

 age, just before Man, excepting the small patches of Lower Helder- 

 berg near Montreal. This region of dry land spread eastward from 

 Montreal to the Green Mountain region in western New England. 

 Thus, the St. Lawrence channel, which was first a short strait between 

 the Archaean areas of Canada and New York, had become much nar- 

 rowed and lengthened 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. 



4. Some characteristics of the force engaged. — The cause of 

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

 following characteristics : — 



1. The force acted at right angles to the course of the flexures, and, 

 therefore, approximately to the general direction of the eastern New 

 England coast. — 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. The force was slow in action and long continued. — That the 

 movement must have been slow in progress, the flexures a gradual re- 

 sult of a movement not exceeding a few feet or yards in a century, 

 continued through a very long time, is evident from the regularity 

 which the stratification now presents, notwithstanding 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 fracture, except in the neighbor- 

 hood of the axes of the folds, where the strain was greatest. There 

 may have been sudden starts, and earthquakes beyond modern experi- 

 ence ; but the general course of progress must have been quiet. 



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

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



