1853.] BIGSBY GEOLOGY OF QUEBEC. 87 



The following description of the new species of Graptolite has been 

 kindly supplied by Mr. Salter. 



DiDYMOGRAPSUs CADUCEUS, Salter. Fig. 1. 



D. stipite filiformi longo ; ramis retrorsum flexis, fere parallelis ; rachide utroque 

 latiore, dentibus prominulis, appendice nullo. 



This form is closely related to D. geminus, Hisinger ; but th6 two 

 branches are bent so much back, as to be nearly parallel, and the 

 stalk is very long and threadlike. 



From the Lauzon precipice. 



Fig. 1. — New species of Graptolite, Didymo- 

 grapsus caduceus, Salter, from the Lauzon 

 precipice {Hudson River Group). 



Local geological Notices. River Montmorenci. — Since the Falls 

 of Montmorenci and their vicinity aiford good sections of all the 

 rocks of the district, I shall commence my local descriptions there. 



The River Montmorenci, after issuing from the adjacent forest- 

 hills, traverses some broad gravelly meadows, in the midst of which 

 a few ridges or reefs of gneiss give rise to a low cascade, called " The 

 Three Leaps," about three miles from the St. Lawrence. 



One mile and a half below this cascade the river cuts through a 

 barrier of limestone half-a-mile across, at what are called the " Na- 

 tural Steps," — a very narrow gorge, whose sides are either mural or 

 worn into the form of stairs or steps. 



One-third of a mile below the Natural Steps is a bridge, and a few 

 hundred yards lower down, the noisy river (its banks always high and 

 rocky) plunges into a small round cove of the St. Lawrence, 228 feet 

 below. 



Gneiss is the lowest visible rock ; and from below the Natural 

 Steps it floors the river with reefs, peeping also from beneath the 

 whole east bank down to the bridge, as well as in spots along the 

 west bank. A few hundred yards E.N.E. of the bridge also, the 

 gneiss emerges above the herbage in the fields, and, gradually attain- 

 ing greater height and breadth, runs E.N.E. to join the mountains 

 in the rear, and in a line nearly parallel to the St. Lawrence. 



The Falls pass over a great cliff of gneiss which forms the centre of 

 the cove which the falling waters have scooped out of the banks of the 

 St. Lawrence ; and its flanks are formed of sedimentary rocks, which 

 are greatly, but not wholly, obscured by gullies, dislocations, talus, 

 and vegetation. The strike of the gneiss is south-west, in broad flakes 

 with frequent flexures ; and the dip, when not vertical, is to the S.E. 

 Potsdam sandstone rests upon gneiss horizontally, and therefore un- 

 conformably ; itself supporting Trenton limestone. 



The sandstone is plentiful on the east bank of the river, above the 

 bridge, and is a yard and more thick, as well as on the west bank 

 both above and below the bridge ; the plane of contact with the 

 enclosing rocks being clean and abrupt It is white, brownish-red, or 



