[Footnote 12: Certain river mouths and estuaries in the north of Scotland "within flude-marke of the sea," have lately given rise to various questions of disputed rights regarding the erection of stake-nets, and the privilege of catching salmon with the same. These questions involve the determination of several curious though somewhat contradictory points in physical geography, geology, and the natural history of fishes and marine vegetation.] That salmon return with great regularity to the river in which they were originally bred, is now well known. Mr Scrope, however, thinks that they do not invariably do so, but will ascend other rivers during spawning time, if they find their own deficient in bulk of water. Thus many Tweed salmon are caught in the Forth, (a deep and sluggish stream,) and a successful fishing there is usually accompanied by a scarce one in the Tweed. Yet we know that they will linger long, during periods of great drought, in those mingled waters where the sea "comes and gangs,"--as was well seen in the hot and almost rainless summer of 1842, when the Berwick fishings were abundant, but those of Kelso and the upper streams extremely unproductive. The established fact, however, that grilse and salmon, under ordinary natural circumstances, do certainly return to their native beds, is one of great practical importance, because it permits the plan of peopling barren rivers by the deposition of impregnated spawn carried from more fruitful waters. It ought to be borne in mind, however, in relation to this latter point, that these waters must possess, in a considerable measure, the same natural attributes which characterize the voluntary haunts of salmon. If they do not do so, although the fry bred there will in all probability return thither from the sea as grilse, yet the breeding process will be carried on at first feebly, and then inefficiently, till the species finally becomes extinct. The same observations, of course, apply to trout. It has been proposed, we believe by Sir W.F. Mackenzie of Gairloch, to apply the principle of one set of Mr Shaw's experiments to the improvement of moorland lochs, or others, in which the breed of trout may be inferior, by carrying the ova of a better and richer flavoured variety from another locality. Now, in this well-intentioned scheme, we think there is some confusion of cause and effect. It is the natural difference in food, and other physical features and attributes, between the two kinds of lochs in question, which causes or is intimately connected with the difference in the fleshly condition of their finny inhabitants; and unless we can also change the characters of the surrounding country, and the bed of the watery basin, we shall seek in vain to people "the margins of our moorish floods" with delicate trout, lustrous without any red of hue within, in room of those inky-coated, muddy-tasted tribes, "indigenæ an advectæ," which now dwell within our upland pools.