202 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 24, 



than others, are still characterized by Scolithus, and the more massive 

 beds hold abundance of two species of Maclurea, — M. matutina of 

 Hall, and a new species. The strata are nearly flat ; and, seen at 

 intervals, they continue so for about six miles to the bridge on the 

 Chateauguay River, in the first two miles of which the same two spe- 

 cies of Maclurea are met with in several exposures, while the litho- 

 logical character of the rock varies little the whole way. An exposure 

 near the bridge displays Pleurotomaria rotuloides of Hall (a Trenton 

 species) . In beds of good limestone *, three miles farther east, and in 

 the Caughnawaga quarry two miles beyond these, occur Atrypa 

 plena and Orthis pectinella. Four miles farther on, at St. Louis 

 Rapids, the rock contains nine species belonging to the Trenton for- 

 mation. They are Leptcena sericea, L. deltoidea, Orthis striatula, 

 Lingula quadrata, Murchisonia hicincta^ Glyptocrinus decadactyhis^ 

 Echino-encrinites anatiformis^ Calymene senaria, Isotelus gigas, be- 

 sides the genera Stromatopora, Orthoceras, and an unfigured species 

 of Encrinurus. Beyond this the Utica slate appears below the St. 

 Louis Rapids, and, crossing the St. Lawrence, can be traced along 

 the shore of the Island of Montreal to the city, displaying Triarthrus 

 Beckii and Graptolithus hicornis in many places. 



Passing westward from the track-bed near the mouth of the Beau- 

 harnois Canal, the sandstone can be followed with little intermission 

 for a distance of three miles up the St. Lawrence, where it becomes 

 interstratified with calcareo-arenaceous layers ; but at St. Timothy, 

 three miles farther, sandstone beds, holding Scolithus, are still met 

 with, and Raphistoma occurs in Calciferous Sandrock. For between 

 four and five miles farther up the river the strata are concealed by 

 drift, until reaching Grande Isle, where quarries expose good limestone 

 beds, resting horizontally on others of an arenaceous character, and 

 containing Raphistoma (two species), Murchisonia, Euomphalus, and 

 Leperditia canadensis-f (Jones, MS.), all unfigured ; and at the 

 head (western end) of the Beauharnois Canal, three miles farther up, 

 besides Raphistoma there is a Phacops, allied to P. BowningicBj and 

 Isotelus gigas (the latter belonging to the Chazy limestone). All 



* In a communication from Mr. Logan, dated at Montreal, July 6, 1852, it is 

 directed that the boundary-line of the Chazy and Trenton limestones between the 

 bridge on the Chateauguay River and the St. Louis Rapids should be removed to 

 about a mile east of the position of Caughnaw^aga. It being too late, how^ever, to 

 correct the map, this emendation is here referred to. Mr. Logan also observes, 

 with regard to the Island of Montreal and the district eastward of the Riviere du 

 Nord, where the colour is made to die out, that he is now examining the unrepre- 

 sented part of the country which is in the vicinity of this shading off, and he finds 

 that the Chazy limestone comes nearly up to the Montreal Mountain (green on 

 the Map), thus displaying very distinctly the trough of which the deepest part is 

 under the Utica Slates of the \Vhite Horse Rapids. 



By too much colour on the Map, the Trenton limestone of the White Horse 

 Rapids is shaded off into the Chazy hmestone of Montreal. 



We have also to remark that the district coloured yellow should be designated 

 as ** Hudson River Group, covered with Tertiaries and Drift." 



t Occurring also at Hawkesbury, Grenville, and Loucks Mills (wrongly spelt on 

 the Map), on the Castor River. 



