igo2] Ami Field Notes. 149 



FIELD NOTES ON THE GEOLOGY OF THE COUNTRY 

 ABOUT CHELSEA, QUEBEC. 



O. F. N. Club Excursion, Chelsea, Sept. 5TH, 1902. 



Several interesting g-eolog^ical phenomena were examined along 

 the 'alley of the Gatineau River on Saturday afternoon September 

 6th, 1902. 



Along the western side of the falls and rapids at the Island 

 east of Chelsea Station on the C. P. R., the Arch^an crystalline 

 rocks consist for the most part of irregularly broken and shredded 

 bands of rusty gneiss, whose strike was almost directly east and 

 west, and at right angles to the course of the river, through which 

 were injected several dykes of coarsely crystalline granite afford- 

 ing excellent examples of graphic granite, microperthite and peg- 

 matite. These are evidently of later date and origin than ihe 

 foliated gray shredded gneisses. The water of the falls and rapids 

 tumbles from a hard ledge of finely twisted and banded hornblendic 

 gneiss on a softer band of pyroxenite with numerous crystals ot 

 mica, mostly biotite, in which are segregated veins of quartz with 

 fibrous hornblende and hematite. Molybdenite crystals were 

 elsewhere observed in masses of rock from this latter band and 

 collected by members of the Club and of the Normal School. 



Several pot-holes occur in the softer pyroxene rock of the 

 bottom ot the falls showing the erosive action of streams carrying 

 detrltal matter in their ru>hing waters. One of these was fully four 

 feet in depth. The river bed is for the most part rocky at this point. 

 At different levels, however, below high-water mark the geological 

 party observed --ecent accumulations of sand, gravel and boulders 

 along the shores and en the rocky surfaces of the river bed, which, 

 at this time of the year, are exposed on account of the low water. 

 Accumulations of sands arranged concentrically to the shore 

 line are found in the bays of a semicircular shape and usually at 

 the foot of a prominent ridge which extends into the river and on 

 the lower side of the ledge forms an eddy by the rapid and sud- 

 denly arrested flowing waters. The sorting power of water was 

 well exemplified in the different accumulations of sand observed. 

 Not less than five zones or series of sand bands were seen at 

 different levels above low water mark, in which the materials 



