LOCALITIES. 87 



lumpy, with few interstices or cavities in which water 

 will constantly lie ; and presenting to the waves sloping 

 ridges, along which the water freely runs up and down, 

 very few species of sea-weeds, and these only of the 

 coarsest kinds, are commonly to be met with. And thus 

 the vegetation of granitic shores may be characterised as 

 poor. But this poverty is owing altogether tp outward 

 form. For, wherever the granite affords a tolerably flat 

 surface, interspersed with deep cavities in which pools 

 of water are constantly maintained, a vegetation will be 

 found as varied and copious as on stratified shores of a 

 totally different composition of rock. The best locali- 

 ties are those in which there are the greatest number of 

 rock-pools of moderate extent, with perpendicular sides, 

 and a depth varying from one to three feet. Pools of 

 this character, though situated near high-water-mark, 

 so as to communicate with the sea only when the tide 

 is near its height, often produce all the species which 

 are considered to be characteristic of extreme low-water- 

 mark. Their depth is sufficient to keep the water at a 

 sufficiently even temperature, and then* steep sides afford 

 that shade which the more delicate sea-weeds require. 

 On chalky shores I have observed that sea-weeds are 

 poor, and few in number. And this I attribute chiefly 

 to the general absence of such rock-pools, though no 

 doubt the soft nature of the rock has its influence, and 

 the white surface, reflecting a greater quantity of light 

 than the more delicate Floridece can endure, drives 

 such species to a greater depth of water on chalky 

 shores than on others, and thus beyond the influence 

 of the tide, or the reach of the botanist. The frequent 



