Ix Proceedings of the Botanical Society 



It will be evident that with a receding flood tide it is quite pos- 

 sible, nay, even probable, that such markings would be made on 

 stretches of mud or sand along a shore, and if the next tide did not 

 obliterate the trails formed by the sea-weed carried stones on the 

 upper part of the beach, most probably these markings, exposed for 

 a time to the sun, would harden, and this operation would go on 

 from tide to tide, until a considerable part of the shore would be 

 covered with the markings, and, when another series of flood tides 

 came, the now firm moulds would be filled up with layers of fresh 

 sand or mud, and might thus remain for ages, until some enthusi- 

 astic geologist broke up the matrices and found a new wonder. 



Subsequent investigations have shown us that the tracks are not 

 soon obliterated upon the sand, and during calm weather will 

 remain for several days quite distinct, though their sharp outlines 

 become less clearly defined after each tide. It is also well to 

 remark that the difference of the height to which spring and neap 

 tides rise here is very considerable. 



But to return to the strand of Oransay ; let us say, that having 

 now got the clue to the cause of the markings, we found that there 

 was an immense number of stones thus travelling westwards and 

 eastwards, and that they varied much in weight, those we saw 

 moving being from a few ounces to half a hundredweight, but we 

 observed at various parts isolated boulders that we judged would 

 each weigh several hundredweights, and these we think must have 

 been carried there by sea-weed. 



The quantity of rock thus carried out to sea by each tide is very 

 great, and we believe, must weigh many tons ; and if this movement 

 is in constant operation even for a few weeks or months of each 

 year, it must be a most important factor to be kept in mind in con- 

 sidering the physical changes that are in operation in this part of 

 Scotland. And if this is likely to be the case, when Ave consider 

 such a narrow channel as that between Colonsay and Oransay ^ what 

 must it be if a similar force is working all along the west of Scot- 

 land? and if you extend the field for consideration, how much 

 greater the effects ] 



The sea-weeds attached to the stones were principally of the 

 tribe Fucidse, and those we noticed most were Fucus nodosus, 

 serratus, and vesiculosus ; each of these varieties of sea- ware has, 

 with regard to high water mark, its own zone along sea coasts, but 

 conjointly they cover wherever they occur the whole beach from 

 high to low water mark, and may be arranged as follows : — 



1. Fiicus nodosus — high water to half tide. 



