WILDFOWL OF THE NOETH-EAST COAST. 165 



snugly tucked away among their back feathers. Many of 

 these modifications of the habits of wildfowl during severe 

 weather, and especially the precise causes which tend to pro- 

 duce them, are a most interesting subject for investigation. 



The sand-flats, just described, afford one main factor in 

 bringing about the altered physical conditions which then 

 prevail. Over these vast dead-level expanses of wet sand 

 there is spread a thin covering a mere film of salt water, 

 either left by the tide or blown up by the wind. In severe 

 frost this film freezes into a sheet of ice, so thin and elastic 

 (or pliant) as to rise with the succeeding tide, unbroken ; 

 with every ebb its thickness increases. Then, perhaps, comes 

 a snow-storm, and the surface of the ice is covered three or 

 four inches thick with snow. This rapidly freezes to the ice 

 below, and, in fact, forms a compact and homogeneous mass 

 with it. Thus in the course of a severe three days' frost 

 there is formed on the sand-flats what can only be described 

 as one vast ice-field, of perhaps many hundreds of acres in 

 extent, and five or six inches in thickness. The weight of 

 the ice gradually causes the solid field to split and crack up 

 on the flood-tide, the chief breakages occurring along the 

 outer side, where the water is deepest and the influence of 

 the tideway most felt. The whole ice-field also tends to drift 

 outwards on the ebb, and, as long as the frost holds, the 

 process of congelation and the creation of new ice continues, 

 and goes on afresh. Thus very great quantities of ice are 

 carried off the flats by every ebb, while the places left vacant 

 are being rapidly reoccupied by a further generation of glacial 

 supplies. 



Even in a frost of but a few days' duration the quantity 

 of ice thus daily set afloat by the tide is very considerable. 

 But when, as happens in such extremity of cold as we ex- 

 perienced in the winters of 1878-9, and again in January, 

 1881, the frost continues unbroken for weeks at a time, the 

 phenomena created thereby are indeed almost incredible, save 

 to those who have witnessed them. The masses of de- 

 tached ice, split up by their own weight into fragments of 

 all sizes and shapes, and carried here and there by the cur- 

 rents, drive helter-skelter in the tideway, and along the lee 



