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«8 



CANADIAN FOSSILS. 



diately succeeding or Salina epoch, there seems to have been a uniform 

 elevation, leading to the prevalence over the same area, of shallow waters, 

 liable in part to actual desiccation. Toward the close of the period, as in 

 the like portion of each of the great cycles of American Palaeozoic history, 

 subsidence again occurred, and the marine limestones of the Lower Hel- 

 derberg (Ludlow) formation overspread a still wider area in the eastern 

 part of the continent than did those of the Niagara. Hence we find the 

 marine beds of the Lower Helderberg rising high on the slopes of the 

 Appalachians, while such patches as that of St. Helen's Island near 

 Montreal * show that they at one time covered the Lower Silurian plain of 

 Canada. The subsidence which enabled them to do this, was apparently 

 accompanied by the ejection of the trappean masses which penetrate the 

 Lower Silurian beds, and among the fragmentary debris of whose bases 

 the remaining portions of Lower Heldorberg limestone have in some 

 places, as near Montreal, been entangled and preserved. In like manner, 

 in Gaspd, in Anticosti, in New Brunswick, in Nova Scotia ajid in Maine, 

 ■we have the extension of the same Lower Helderberg sea, proved by its 

 fossiliferous deposits. And though, as I have elsewhere observed,! *b® 

 fossils of the Nova Scotia rteks of this age, (Arisaig group) show a ten- 

 deacy to European rather tlian to American types, this merely indicates 

 the partial interruption of the continuity of the great oceanic area, by the 

 remaining shoals of the Appalachian ridge. It would thus appear that at 

 the close of the Upper Silurian, the area of land in Eastern North America 

 was at a minimum ; being probably less than at any preceding period since 

 th« deposition of the great Trenton limestones of the Lower Silurian. 



At the beginning of the Devonian a slow and gradual emergence, 

 not accompanied by any fractures or physical disturbances, appears to 

 have commenced. The wide spread of the Oriskany sandstone, and its 

 accompanying arenaceous beds, indicates this change. This re-elevation 

 was earlier and more permanent near the Atlantic coast than farther 

 inland. "West of the Appalachians, the Comiferous limestone, probably the 

 finest coral limestone in the American Palaeozoic serie3, indicates a wide 

 internal ocean ; while in Gasp€, New Brunswick and Maine, its place is 

 occupied by beds filled with land-plants, and some of them even under- 

 clays or fossil soils, like those of the Coal-formation. Similar conditions 

 followed somewhat later in the West ; and the Comiferous limestone was 

 covered with the shales and sands of the Hamilton and Chemung series, 

 during the deposition of which the condition of all North America must 

 have approached to that which it afterwards assumed in the time of the 



• Report of Geology of Canada, 1863. 



t Acadian Geology.— Sec also paper by Dr. Honoyraan, in Journal of Geol. Society, 



