of Edinhurgh , Scssioji 1880-81. Ixi 



2. Fucus serratui; — about half tide. 



3. Fiicu-s vesiculosii-s — extending from near high tide to low water 

 mark. 



But as Fucus serratus is devoid, or nearly devoid, of air vessels, 

 it may be left out of account for our present purpose. 



It Avill be seen that with Fucus nodosus and vesicidosus we have 

 a growth of sea-weed extending from high to low water mark, and 

 that for part of that distance these two weeds intermingle; and it 

 is quite possible to find both varieties growLag upon the same stones. 



You will also bear in mind that both of these sea weeds are 

 supplied with air vessels which float the weed with the rising tide ; 

 and so great is the buoyant power, that loose stones to which the 

 Fuci are attached are raised from their beds and floated, the 

 current transporting them in whatever direction it may set. 



The result of the continued action of this carrving force will be 

 to denude our coasts of much of the detached and broken rock 

 around them ; and if these fragments are carried out to sea, floated 

 by these vegetable buoys^ they will ultimately be deposited at the 

 bottom of the ocean, for periodically the sea-weed will decay ofi", 

 and then the stones freed from their floats will siuk. 



These individual stones as units may seem insignificant factors in 

 the physical changes continually going on, but in the aggregate they 

 represent a mighty force filling up the ocean bed. But this is not 

 all ; for we have evidence that another and perhaps more important 

 operation is going on as regards the position of sea and land. 



Our observations led us to notice that at a place where a stone 

 was left by the receding tide it sank, and that aU except flat stones 

 went downwards until they were checked by the resistance offered 

 by the sand to the great surface of the attached masses of sea-weed. 

 Most of the stones which thus rest in transit across the strand rise 

 with the succeeding tide, but at certain seasons, we believe, many 

 siuk in the sand to rise no more, owing to the attached sea-ware 

 either rotting off or losing its buoyant powers, and stones thus 

 deposited are slowly but surely forming a barrier, which will in 

 time become an isthmus between Colonsay and Oransay ; then we 

 shall find the latter island as a peninsula to the former, and as the 

 sand accumulates on each side of the isthmus, it will gradually 

 increase in breadth, until instead of being a peninsula, Oransay 

 shall really form a southern point to Colonsay.* 



Having been led to this conclusion, we made inquiries among the 



* At times a portion of the sand upon the strand changes its position, and 

 the deposited stones can then be seen. 



