286 THE ZOOLOGIST. 



have a special tidal range of movement. Beginning at low 

 water at the western-most feeding-place, they move eastward by 

 stages, according to the tide, each of the three main feeding- 

 places being adjusted to a certain state of the tide, and end 

 towards high water at the eastern-most part of their range — 

 on the refuge of Eyebroughty. The sequence is reversed on 

 the ebb. 



B. Drum Flats Station. The two previous examples of the 

 mud-flat habitat are enclosed in small estuaries, debouching in 

 the one case into the North Sea, in the other, into the estuary of 

 the Forth. The Drum Flats, now to be described, border the 

 Forth itself, and form on the southern shore the lowermost part 

 of the continuous mud-beaches of the upper estuary. The mud 

 is light and shifting in places, more tenacious in others. Weed 

 is luxuriant. Bordering the channel of the Eiver Almond the 

 mud is firmer, and large areas afford an abundant and good 

 supply of Mussels. The feeding area lies more than 150 metres 

 from the land. A large stock is resident in winter. A range of 

 tidal volcanic rocks lying to the west of Granton Harbour and 

 well off shore is covered with Mussels in the absence of weed, 

 and is much visited by the settlement. Cramond Island, lying 

 at the mouth of the Almond Channel and close to the principal 

 feeding area, is inhabited. The Oystercatchers do not resort to 

 it. The refuge is on the Islet of Inchmickrey, lying on the 

 middle bank of the Firth of Forth. The exposure is not severe. 



4. Rock-beach Habitat. — Of the four stations of rock-beach 

 habitat coming under observation, one (Eyebroughty) will be 

 described in some detail, and only the factors by which the 

 others differ from the Eyebroughty station will be mentioned. 

 In the Eyebroughty station a long tidal reef, lying to the west 

 of Eyebroughty, and about 450 metres from the mainland, 

 provides quantities of Mytilus, for the most part of small size. 

 The settlement feeds here a good deal, but the foothold is only 

 moderately good, and in storms the reef is wave-swept. Near 

 Cheese Bay there are two large bosses of volcanic rock lying 

 well off the land. They are crowded with Mytilus of small size, 

 and are visited daily. At the east end of Bedhouse Bay there 

 is a flat, low-lying rock forming a horn to the bay. The outer 

 part carries a moderate stock of small Mussels. Part of the 



