290 



The Scottish Naturalist. 



THE PLOEA Of EIVER-SHINGLES. 



By F. Buchanan White, M.D., F.L.S. 

 LL rapid rivers have a tendency to form, at various parts of 



XX their course, the accumulations of water-rolled stones 

 known as shingles or stanirs (staners or stanners). The latter 

 term, though applicable to all collections of small stones and 

 gravel on the margin of a river or lake, is perhaps more generally 

 used for those island-like beds — frequently or occasionally dry — 

 which lie in the channel of a river. 



These shingles or stanirs are objects of much interest both to 

 the geologist and to the botanist — to the geologist on account of 

 what may be called their life-history, that is, their origin, growth, 

 and decadence ; to the botanist on account of their flora. 



A river if left to itself is perpetually altering its course. It 

 flows in curves; and denudes one bank, and piles up debris on the 

 other. The debris thus accumulated forms shingles or stanirs ; 

 and if nothing occurs to induce an alteration in the direction of 

 the current the shingles continue to grow. But, perchance, in the 

 course of denudation a big stone or a rock, or even a harder bed 

 of gravel may be met with, and may prove an obstacle to the con- 

 tinuance of the denudation of that bank. The result is that the 

 direction of the current is altered ; denudation of the hitherto 

 wasted bank ceases, and is transferred to the shingle ; and a new 

 shingle is formed on the opposite bank a little below the obstacle 

 which has given rise to the alteration in the current. It thus 

 happens that, unless there is an interference by human agency 

 with the course of a river, the existence of any particular shingle 

 may be brought to an end at any time by an apparently trivial 



At first a shingle or a stanir consists of bare rounded stones 

 more or less submerged for the greater part of the year. By 

 degrees more stones are piled up, and finer gravel and sand obtain 

 a lodgment in the interstices. Seeds are brought to the shingle 

 by the water or by the wind; and the plants thus introduced have 

 a chance of growing during those summer months when the river 

 is low, and the shingle unsubmerged. Their stems and branches, 

 — either dead or alive, — serve to detain more debris during the 

 next flood ; and thus by degrees the shingle grows, and its 



cause. 



