IN THE UNITED KINGDOM AND FRANCE. J 67 



especially of plants and sedentary animals. Strong currents also act 

 in another way, they carry along a quantity of suspended matter which 

 is injurious to sedentary animals. 



The nature of the soil of the shore and sea bottom is intimately con- 

 nected with currents and the moving power of water. The suspended 

 matter brought down by rivers, and the matter derived from the gradual 

 eating away of the coasts are deposited in accordance with three causes : 

 size of the suspended matter, its specific gravity, and its form ; that is, 

 the largest, densest, and roundest particles are those first deposited. Loose 

 matter is lifted up by moving water in accordance with similar laws ; 

 namely, the smallest, least dense, and roundest fragments are first moved ; 

 the largest, densest, and flatest last. The effect of these laws is that the 

 loose matter of shores is sifted and sorted, and the same thing happens with 

 the suspended matter of rivers. In one place we find, according to the 

 velocity of the currents, the shingle, in another the sand, and in a third 

 the mud. But not only is gravel separated from the sand, and the latter 

 from the mud, the round rolled gravel is not mingled with the flat 

 shingle, or the granular mud with the highly hydrated unctuous clay, 

 provided the motion of the water has been sufficient to permit of the 

 loose materials being thoroughly sifted. By the action of the variable force 

 of tidal currents, this kind of perpetual sifting of the loose materials of sea 

 coasts and sea bottoms is always going on. Each kind of material thus 

 sifted out has its own fauna and flora. Submarine rocks sheltered from the 

 violence of the waves and the force of currents, and favourably circum- 

 stanced as to temperature and sunlight, are always covered with a rich 

 vegetation and peopled with varied forms of animal life. Mud when 

 sheltered from the disturbing action of the waves, or when sufficiently 

 consolidated not to be moved at every rise and fall of the tide, becomes 

 covered with vegetation and sedentary animals. On the other hand, no 

 vegetation fixes itself on fine mud which is continually being moved by 

 the rise and fall of the tide. The only animals which can live on such a 

 mud bank are annelides, and other creatures which bury themselves in 

 it. This is also the case where the suspended matter of rivers continually 

 deposit fresh layers of mud, even though the deposited mud may not be 

 again disturbed. Those mollusca and annelides which can bury themselves 

 below the line of tidal disturbance of the sand, can live on sandy shores 

 even in shallow waters ; but scarcely any form of animal life can exist 

 on a shingle shore. Even the slightest change in the angle of declivity 

 of a sandy beach alters the conditions of animal life, and consequently 

 more or less affects the fauna. 



Independent of this general effect which the mechanical constitution of 

 the shore and littoral sea bottom has on marine plants and sedentary 

 animals inhabiting it, the nature of the soil, conjointly with the other 

 causes above enumerated, by the influence which they exert on the food 

 of plants and animals, produce a marked action on the character of the 

 flora and fauna, that is, upon the association of species. 



Even upon the individuals of the same species of animal the soil is 

 found to exert so great an influence that fishermen can often distinguish 

 the individuals from different localities, even from places not far removed 

 from each other. This is especially the case with oysters, the shape, 

 size, colour, and flavour of which are almost as various as those of fruit 

 or tobacco grown on different soils. Were we able to determine the 

 specific qualities of the soil which produce those differences in the quali- 

 ties of oysters it would be an important step in their cultivation. Again, 

 soils favourable for the reproduction of the oyster are not always equally 

 favourable for their subsequent development ; and again, there are 

 many places, where oysters thrive, but where they cannot breed. This 



