138 PLANT-LIFE ON LAND [ch. 



{Elymus arenarius), which shares many of the 

 characters of the Marram, and the Sea- Couch Grass 

 (Trlticum junceum). But these are neither of them 

 so successful, the latter together with the Sand-Sedge 

 {Gar ex areiiaria) being deficient in capacity for 

 upward growth after being buried in the driven sand, 

 in which respect the Marram especially excels. 



The White Dune thus formed is sometimes styled 

 the Shifting Dune. Having its sand retained only 

 by entanglement amongst the relatively lax growths 

 of the Marram, its surface is liable to be blown away 

 again, while the sand removed from the windward 

 side will be caught by the vegetation on the sheltered 

 side. More especially does this occur where the Dunes 

 have attained great height, for there not only are 

 they more exposed to the wind, but also the plants, 

 being higher above the level of the ground- water, are 

 apt to grow less strongly, and form a less efficient 

 protection. And so the whole Dune may appear to 

 change its position, advancing by degrees down the 

 prevailing wind. There is probably no better example 

 of this in Great Britain than that of the sands of 

 Culbin near Forres, on the south coast of the Moray 

 Firth. Moreover the history of that strange waste of 

 sand is so far known that an additional interest springs 

 from it. The estate of Culbin, extending to some 

 3600 acres, was in the l/th century celebrated for 

 its fertility. It^was intersected by the river Findhorn, 



