544 



HISTORICAL GEOLOGY. 



division of the Salina. The thickness of the shale and limestone varies from 150' to 235'. 

 (J. J. S.) 



(c) Eastern Bonier region. — The Niagara limestone occurs in eastern Canada, some 

 distance south of the St. Lawrence, being part, according to Logan, of an extensive for- 

 mation, which stretches from northern Vermont, eastward over a part of northern New 

 Hampshire and northern Maine, to Cape Gaspe on St. Lawrence Bay, as limestone with 

 some massive and shaly sandstone. The formation embraces also the strata of the Lower 

 Helderberg, and possibly part of those of the Lower Devonian. Niagara fossils occur ia 

 the lower part of the Gaspe limestone, as well as at some intermediate points. They 

 have been found also near Penobscot Bay. 



At Arisaig, in Nova Scotia, there are shales of the Niagara epoch, 1300' thick ; and 

 they occur also in New Canaan and Pictou. 



(d) Arctic regions. — In the Arctic, the Niagara limestone has been observed between 

 the parallels of 72° and 76°, on the shores of Wellington and Barrow straits, and on 

 King William's Island. The common chain coral Halysites catenulatus has been found 

 at several localities, along with various Upper Silurian species, and also at other places 

 between 79° and 82° N. 



LIFE. 



739-743. 



T42 



1. Plants. 



Supposed Algae or Fucoids, of branching form, of the genus Buthotrephis, 

 occur in the Clinton group. They are various rounded casts looking like 

 those of stems, or groups of stems, some of which are probably tracks of 

 marine animals, as already explained. 



2. Animals. 



In the Niagara series no evidence of fresh-water or terrestrial species of 

 plants or animals has yet been observed. Aquatic Vertebrates or Fishes 



have been reported from the Clinton beds. 



The Medina beds contain few fossils. These are 

 chiefly Brachiopods and Lamellibranchs, with rarely 

 Gastropods and Cephalopods among Mollusks. Tracks 

 of Sea- worms are common, because the beds are of mud- 

 flat and sand-flat origin. The Clinton group has more 

 ^j) »J (^il=s^lii*, n^ii^erous fossils, of the same general character, and 



partly the same species ; but as it includes limestone 



beds, there are also Polyp-corals, Bryozoans, and Trilo- 



bites. The Niagara beds, which were largely formed in 



clear, open seas, contain a profusion of fossils of marine 



types : Bryozoans, Polyp-corals, Crinoids of various 



Mediha. — Fig. 739, Linguia fomis, Brachiopods iu great numbers, and various kinds 



cuneata; 740, Modioiopsis of Mollusks, witli many suiall and large Trilobites. 



genia ; 742 pieurotomMhi '^^^ most comuiou of Medina Brachiopods is the 



litorea ; 743, Bucania trUo- Lingula cuneuta, Fig. 739, a wcdgc-shapcd species. 



Figs. 740 and 741 represent Lamellibranchs ; and 742, 



743, Gastropods, the last a Bucania. 



