MacMillan : shores at lake of the woods. 1015 



boulder strand may be termed gravel-beach for this is the 

 form it usually takes. 



I. Gravel-beach. Upon beaches that are composed alto- 

 gether of a coarse gravel the pebbles are so readily moved 

 about by the surf that vegetation finds great difficulty in estab- 

 lishing itself. Consequently the area of a gravelly beach 

 nearest the water's edge is commonly quite sterile. Not even 

 do pools of algae find it easy to become established. Farther 

 back, however, scattered herbs and shrubs can gain a foot- 

 hold. The segregation of pebbles that goes on under the lap- 

 ping of the waves, or under surf impact, is such that the 

 smaller are often thrown well inland while the larger are left 

 upon the extreme front of the shore. Consequently a strip of 

 small grasses and herbs usually occupies the shoreward por- 

 tion of the strand, and these plants, that are thus established, 

 are strongly lithophytic in character. Hence upon such 

 gravelly beaches one finds Campanula and Heuchera in great 

 profusion, together with Agrostis, Ambrosia and Omagra, a very 

 different population in its appearance from that of sandy 

 beach. Still farther back a group of psammophytes often 

 comes in so that there is strong semblance of zonal distribution. 

 Indeed so far as the plant distribution is affected bj the action 

 of the waves in segregating the pebbles, it is truly zonal. It 

 is classed under the general azonal type because of its 

 habitat and strongly azonal method of development. Upon a 

 new gravelly shore the distribution is quite azonal. The gravel 

 beach may properly be regarded as an intermediate type of 

 formation. 



II. Gravel slopes. Such rounded slopes, covered with Epilo- 

 bium, Onagra and Rhus, are seen on Garden Island. The sub- 

 soil seems to be of sand and clay, and the humus sheet is thin. 

 Yet a group of shrubs, developed in quite irregular and azonal 

 fashion, are able to establish themselves and persist. Much of 

 the organic matter is drained out of the soil through the sub- 

 soil, and the slopes are, as a whole, where studied, not highly 

 nitrogenous. The number of plant species is therefore limited 

 and consists chiefly of low shrubs. I have seen no lichen or 

 moss-covered gravel slopes, such as are developed from talus. 

 Probably the rounded shape of the pebbles favors more 

 ready drainage-off of organic substances than the irregular, 

 angular shape of the talus fragments. If this be true it is an 

 interesting fact to notice. Evidently the paucity of species, 

 determined by rapid drainage and consequent low nitrogen- 



