BOTANY OF LAKE HURON. 469 



general contour is parallel to the present margin of tlie Lake. Con- 

 forming to tlie irregularities of the coast for about sixty miles, and 

 at an average distance from it of a mile and a half, it reaches on the 

 south the sandy flats of the Kivi^re aux Sables (south), and is finally 

 lost. The western slope of this lacustrine terrace inclines gradually 

 towards the present Lake beach, and within this limited area deposits 

 of shell-marl are frequently found. Future researches will, no doubt, 

 prove the existence of other terraces lying more to the eastward, 

 which will, doubtless, throw much light on the former physical 

 features of this Lake-area. Hydrographically, the region under con- 

 sideration may be divided into two, more or less, distinct areas, the 

 one comprising the valleys of the Riviere aux Sables (north and 

 south), the Bayfield, Maitland, and Saugeen Rivers which flow into 

 Lake Huron ; the other comprising the bight of Owen Sound, fed by 

 the Rivers Potawatamie, Sydenham, and Indian, and the Bays Colpoy 

 and Hoj)e. These streams, as a rule, are small, and undergo rapid 

 oscillations of level, increasing in the spring to torrents of considei'able 

 volume, and conspicuously diminishing towards the fall, when, in 

 many cases, numerous small deltas are formed in the lowlands, com- 

 posed for the most part of their alluvial accumulations. 



The hydrographic areas tlivis indicated are naturally separated by 

 the somewhat tortuous escarpment of the Niagara limestone, which, 

 entering this district from the south, sweeps around towards the 

 heights above Cape Commodore, and thence trending northward past 

 Cape Paulet, finally terminates at Cabot's Head, the extreme northern 

 point of the Bruce Peninsula. Throughout its course it conforms 

 with more or less irregularity to the shape of the coast line, but pre- 

 senting a less salient curve, and in every case exposing its precipitous 

 face to the north and north-east, in cliffs I'anging from 50 to 300 feet 

 above the level of Lake Huron. The Clinton limestones, however, 

 are found to visibly underlie the Niagara in the more southern bkiffs, 

 occupying in many instances a vertical face from 70 to 100 feet in 

 height. North of Cape Paulet these limestones disappear, and the 

 cliffs along the coast to Cape Chin are altogether occupied by the 

 Niagara escarpment, and vary in height from 120 to 160 feet. 



Important as is this escarpment from a geological stand-point, it is 

 found to be no less effectual as a meteorological agent, in its relation 

 to the vegetation of this portion of Ontario. The immediate coast 

 along the southern and south-western portions of the Georgian Bay 



