SUMMARY OP THE HISTORY. G65 



from Labrador, a rocky, lifeless continent, in so far as we know. 

 Along its shores are spread out mtiddy bottoms swarming with 

 strange forms of crustaceans and shell-fish ; and, in its more profound 

 depths, are being slowly produced the great coral reefs which are to 

 form the Lower Silurian limestones. In the area i-epresenting the 

 Acadian provinces, shallow waters, invaded by muddy and sandy 

 detritus, appear to have prevailed, with gradual subsidence of the 

 bottom of the sea. 



The Upper Silurian period would seem to have been introduced 

 by new and extensive physical changes, which had the effect of 

 producing greater inequalities of the sea-bottom, and ultimately 

 a deeper sea, though perhaps more limited in area. At this time, 

 also, extensive processes of elevation and disturbance were in pro- 

 gress along the Appalachian chain, and must have tended to sepa- 

 rate more completely the Acadian area from that of the central paii; of 

 North America. These movements were further connected with an 

 entire change of the animal life of the region — a change, however, 

 not sudden but gradual — and in the course of which, it would appear 

 that many species which had long previously existed in other parts 

 of North America, extended themselves over the Acadian area. 



As the Upper Silurian period approached its close, and the sea- 

 bottom had been loaded with many hundreds of feet of arenaceous, 

 argillaceous, calcareous, and ferruginous sediment, another series of 

 physical changes supervened. New lands were thrown up, and — 

 still more wonderful change — these lands were clothed with a rich 

 vegetation ; and the oldest known land animals, delicate and beautiful 

 insects — water-born but air-dwellers — flitted through its shades. 

 With these changes came another and even more thorough revolution 

 among the living things of the seas. 



But while the Devonian rocks were being built up, the older 

 sediments, buried under these newer beds, had been subjected to 

 the intense action of the earth's pent-up igneous agencies; and, at 

 the close of the period, it would seem as if the solid crust had 

 given way, slowly and gradually, to the superincumbent weight, 

 along certain lines ; while in others the edges of the beds were tilted 

 up, and the whole surface of Acadia was thrown into a series of 

 abrupt folds, — great masses of plastic granitic matter invading every 

 opening in the shattered masses. This period surpasses every other, 

 in the geological history of the eastern slope of the American conti- 

 nent, in its evidences of fracture of the earth's crust. To this period 

 we must refer the greater part of the intrusive granites of Eastern 

 America, and to it also is referable the greater part of the mctamor- 



