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MARINE ZOOLOGY which must vary much with the season. Passing down the river to beyond Shoeburyness there is the large flat tract of the Maplin Sands, in some parts 3! miles wide at low water. I have examined this imperfectly off Havengore and at the east end of Foulness. In the Swin, off the Maplin Sands, the water is deeper than anywhere else along the coast of Essex, but yet its maximum depth is only 1 3 fathoms, maintained by the strong tidal currents. Passing westwards along the northern side of Foulness we have the estuaries of the Crouch and Roche, as well as sundry channels and creeks, all having muddy shores, but no extensive flat tracts left dry at low water. In these estuaries and creeks oyster culture is of such importance that hundreds of men are employed, and some of the river beds are worth one hundred times as much as the adjoining meadow land. I am best acquainted with the Crouch, having remained in it off Burnham many times for weeks. When there in summer I have found the low water more salt than the high water, which is an unusual thing in an estuary ; and the water at Battle Bridge, 12 miles from the mouth, more salt than the North Sea, no doubt owing to small rainfall and great evaporation. North of Foulness to the estuary of the Blackwater is a sandy tract left dry at low water for a width of a mile, which I have never examined for marine animals. In the estuary of the Blackwater, often called ' Pont,' I have examined the shores near Bradwell, and have dredged off an island called Osea. Between the Blackwater and the Colne are sundry creeks near West Mersea, and a tract of more or less sandy mud, left dry at low water for a width of ^ mile, the east end of which I have examined to some extent. I have lived in the estuary of the Colne for weeks at a time almost every year for more than twenty years, and have examined the shores and creeks in every direction, and dredged and trawled in the open water off Mersea. On the east side of the Colne, both above and below Brightlingsea, there is good ground for collecting at low water from a boat or in long waterproof boots. Between the Colne and Walton-on- Naze is a long extent of coast with narrow sands, which I have never examined. The open water off this, in the Wallet, is seldom more than 6 fathoms deep, which is no more than in some of the estuaries. On one occasion I dredged in this near the Gunfleet Bank, but in many places the ground is too full of large stones for dredging purposes. The creeks on the east side of Walton-on-Naze are very good collecting ground. In 1889 I remained some time in what is marked on the charts as ' Walton Channel,' but I know nothing of its present condition, since the sewage discharge from Walton was so objectionable that I have not gone there again. But for this it would be the best place on the coast for collecting, since there is no oyster culture and no disturbance by steamboats. East of the Naze is a tract of coast which I have never examined, except near Harwich. Both outside and inside the harbour is or was excellent collecting ground in fine calm weather, but when it is windy little or nothing can be done. Passing up the Stour are vast tracts of mud, covered with Zostera marina, which are left dry at low