33 
NOTES ON THE NATURAL HISTORY 
OF HORNSEA MERE. 
GEORGE BOLAM. 
I went to Hornsea Mere on 20th April, 1912, on behalf of 
the Yorkshire Naturalists’ Union Wild Birds’ and Eggs’ Pro- 
tection Committee, and remained till 2oth July, finding lodgings 
at the East Lodge, Wassand, which is the most convenient end 
of the Mere for observation. The following notes on the 
Natural History of the Mere may, it is hoped, be useful to 
future workers; but they are only the first impressions of a 
stranger to the district, and must not be regarded as anything 
more, nor as in any way exhaustive of the subject. 
The water of the Mere covers about 470 acres. Its surface is 
only about twelve feet above sea level, and nowhere is it deeper 
than ten or twelve feet. Its bottom is, in many places, covered 
by a considerable accumulation of soft mud, but here and there 
it is hard, stony, and ‘clean’; its ridges and islands being 
glacial deposits, in every way similar to those on the adjoining 
land. In several places round its margin there are large solitary 
boulders, chiefly of granite, or porphyry, and many smaller 
ones. Over the muddy parts Fresh-Water Mussels (Anodonta 
cygn@éa) are numerous and of large size; other fresh-water 
molluscs are also abundant. 
There are extensive beds of Reeds (Arundo phragmites), 
particularly at the upper end, varied by large ‘ fields’ of Reed 
Grass, or Manna Grass (Glyceria aquatica), Bullrushes (Typha 
latifolia), and two or three of the common coarse Sedges. Up 
till recently, these beds were extensively cut and used as straw 
for horses, etc..—' Flagging’ being the collective name given to 
the litter in the locality—but the practice has been almost 
wholly discontinued during the last year or two by Captain 
Constable, in the interests of the birds. Outside these beds there 
are considerable extents of Bog Bean, Equisetum, Iris, Pota- 
mogeton, and Yellow Water Lily (a few plants of the white 
Nymphea alba lately introduced in the bay behind the Lady 
Island are doing well, but have not yet spread), with many 
stately clumps of Great Water Dock and other lacustrine 
plants. In the ditches, Water Violet (Hottonia palustris), 
Arrow Head (Sagittaria), and Bladderwort (Utricularia vul- 
gavis) are common, and large corners are filled with tall growths 
of Hairy Willow-herb, Holcus, and other rank-growing plants. 
In the Low Wood, which, since the heightening of the water 
in the Mere, has become largely an almost impenetrable morass, 
trees and herbs are tied together with a tangle of Woody Night- 
shade ; ditches are bordered with tall Canary Grass (Phalaris 
1913 Jan. 1. G 
