J. I>. DANA — AREAS "I CONTINENTAL PROGRESS. 



thickness, as well as the Triassic of Prince Edward [aland. To thia trough 

 the coal formation of Rhode Island and an adjoining part of Massachusetts 

 with its associated Cambrian may belong — as long sine I; for the 



Boundings strongly favor the idea that this Nova Scotia range extends on 

 beneath the ocean's border, and, as recognized by Prof. W. ( >. < Irosby in bis 

 1 ■ ology of Eastern Massachusetts, thai it ha- it- continuation, under 



iund, in tin- Cape < lod ami Plymouth region of southeastern Massachusetts. 



Other approximately parallel Archaean ranges may exist farther eastward 

 in Newfoundland as boundaries "I' Paleozoic troughs; but the published 

 facts do doI enable us now to define them. 



Thirdly. A third range of probable Archaean extends along New Bamp- 

 Bhire, on the easl -id.' of the Connecticut valley, through Massachusetts into 

 Connecticut, dividing the Paleozoic trough of Maine from thai of the Con- 

 oecticut valley; and this Connecticut valley trough ended it- rock-making 

 career, like that of the Bay of Fundy, in the laying down of some thousands 

 of feet of Triassic beds. 



Through these Archaean ranges we thus have the confines of three troughs : 

 The Connecticut valley trough ; that of Maine ami western New Brunswick, 

 extending southward to or beyond Worcester. Mass.; and the Day of Fundy 

 trough, covering eastern New Brunswick and western Nova Scotia and New- 

 foundland, with much of St. Lawreuce Bay, and extending probably far to the 

 southwestward in or beyond the coal region of eastern Massachusetts and 

 Rhode [stand. All three opened northward into the great St. Lawrence 

 Gulf which in early geological time occupied the region of the St. Lawrence 



river valley. 



It i- UOl to lie inferred that Mich troughs were alike from north to south 

 in rock-making. The Connecticut valley trough had thick deposits of 

 Upper Silurian and Devonian rocks laid down in its northern half, which 

 implies deep subsidence, ami at presenl we have no evidence that Bimilar 

 depositions took place in the southern half. It had its thick deposits of 

 Triassic beds in the southern half, which we are quite >m>- did not extend 

 through the northern half. Hut, notwithstanding Bucb independent work 



in the different part-, it was one trough in its Archaean Confines, and in its 



relation- to the general Bystem of progn 



It thus appears thai Archaean operations first established the boundai 

 ami that Paleozoic ami Meeozoic rock-making wenl on in the troughs be- 

 tween these boundary ranges; ami, further, in view of the great thickness of 

 the rocks, that all tie troughs wen- profoundly, ami re or less independ- 

 ently, subsiding 



'flier.- i- this limitation t" the conclusion, that " Paleozoic rock-making 

 went forward within the troughs." The earlier pari of this Paleozoic rock- 

 making, that of the Cambrian and Lower Silurian, went on doI only in tie 



