OF CENTRAL CANADA PART V. 317 



group. The trilobites Asaphus Canadensis and Triarthrus Beckii 

 appear however to be confined to the Utica strata. These range 

 along the shore of Lake Ontario from a little west of Port Hope to 

 a short distance west of Whitby ; sweeping from these points, in a 

 comparatively narrow band, towards the north-west, and coming out 

 on Nottawasaga Bay a mile or two west of Collingwood ; but within 

 the intervening space the formation is entirely concealed by over- 

 lying Drift and superficial deposits. Good exposures may be seen, 

 however, in the vicinity of Whitby, and on the lake shore under the 

 " Blue Mountains " a few miles west of Collingwood harbour. 



The Hudson River Formation consists essentially of shaly thin- 

 bedded sandstones, mostly of a greenish-grey or drab colour but 

 weathering rusty-brown. These shaly sandstones, formerly known 

 as Lorraine shales, are interstratified here and there with a few cal- 

 careous beds. The total thickness of the Formation in this district 

 is about 750 feet. Its fossils are in great part identical with those 

 of the underlying Trenton and Utica beds, these three so called 

 formations forming properly a single subdivision of the Lower 

 Silurian series : dolomitic and other limestones characterising the 

 lower part ; bituminous shales (with more or less distinct fossils) 

 the central portion ; and arenaceous shales, holding many of the 

 lower limestone fossils, the upper part. Some of the mpre common 

 fossils of the Hudson River strata comprise : Climacograptus bicornis 

 (fig. 132); Diplograptus pristis (fig. 132*); Monticulipora fibrosa 

 (fig. 136); Glyptocrinus decadactylus (fig, 154); Galymene Blumen- 

 bachii=C. senaria (fig. 178); Asaphus platycephalus (fig. 168); 

 Trinucleus concentricus (fig. 172) ; Strophomena alter nata (fig. 194) ; 

 Leptcena sericea (fig. 196); Ambonychia radiata (fig. 208) ; Modiola 

 modiolopsis (fig. 209) ; Murchisonia gracilis (fig. 220) ; Bellerophon 

 bilobatus (fig. 221); Cyrtolites (Bellerophon) ornatus ; and Orthoceras 

 crebriseptum (fig. 233). The formation constitutes the shore-line of 

 Lake Ontario from the River Rouge, in the township of Pickering, 

 to the River Credit, west of Toronto. From these points, although 

 much obscured by overlying Drift and more recent deposits, it extends 

 to the north and north-west, and forms the shore of Nottawasaga 

 Bay in the towriships of Collingwood, St. Vincent, Keppel and 

 Albemarle. Good exposures, at most of which fossils may be 

 obtained, occur on the banks of the Humber, Mimico, Etobicoke, 



