Sect. Y, 1922 [49] Trans. R.S.C. 



IX. River-bank and Beach Vegetation of the St. Lawrence River below 

 Montreal in Relation to Water-levels 



By Francis E. Lloyd, M.A., F. R.S.C, and George W. 



SCARTH, M.A. 

 (Read May Meeting, 1922) 



The subject matter of this paper formed part of the evidence in 

 an important legal test case hinging on the question as to the position 

 of high water mark of the St. Lawrence River in the vicinity of the 

 locality here described, viz., the beach below the Imperial Oil Works, 

 near Point aux Trembles, below Montreal. The practical difficulty 

 of determining water levels along a river front is increased by the 

 great variation in range of fluctuation due to local differences of 

 topography, so that a standard range of measurements at one place 

 cannot be applied to another. Nature, however, has provided a 

 series of vegetative zones which, while they may vary in width and 

 vertical range from place to place, always retain their relative posi- 

 tions, and serve everywhere as a natural graduated scale from which 

 to read off not only average high water mark, but all the other seasonal 

 levels also. To classify all the minor topographical variations in this 

 zonal series would require an extended investigation, but a preliminary 

 study of other localities enables us to state that the series here de- 

 scribed is of very wide application and the variations from it apply 

 generally to minor details. 



The river was very low at the time (18 Sept., 1921) the measure- 

 ments were taken. The tension line between the beach vegetation 

 and that of the dry land was placed at eleven feet above the water 

 surface at that time, corresponding to the figure of 24' on the scale 

 at the Lachine canal (assuming that the range of difference between 

 high and low water is the same at the two stations). The close turf 

 formation ends abruptly at this level, which is near the foot of the 

 river bank. It corresponds with the upper limit of Salix longifolia^ 

 as a close formation, only straggling bushes extending further. The 

 occurrence of numerous oil marks (due to floating oil) on branches 

 and stones confirm the view that here the water level remains station- 

 ary for some time. 



The beach vegetation at this station may be divided into four 

 major zones: 



'Nomenclature according to Gray: New Manual etc., 7th ed. 

 4— E 



