These estimates are valuable in various views of our subject. They answer with some definiteness the question so often asked, whether all lands require drainage, and they tend to correct the impression, which is prevalent in this country, that there is something in the climate of Great Britain that makes drainage there essential to good cultivation on any land. The fact is not so. There, as in America, it depends upon the condition and character of the soil, more than upon the quantity of rain, or any condition of climate, whether drainage is required or not. Generally, it will be found on investigation, that so far as climate, including of course the quantity and regularity of the rain-fall, is concerned, drainage is more necessary in America than in Great Britain--the quantity of rain being in general greater in America, and far less regular in its fall. This subject, however, will receive a more careful consideration in another place. If in America, as in Great Britain, one half the cultivable land require drainage, or even if but a tenth of that half require it, the subject is of vast importance, and it is no less important for us to apprehend clearly what part of our land does _not_ require this expenditure, than to learn how to treat properly that which does require it. To resume the inquiry, what lands require drainage? it may be answered-- ALL LANDS OVERFLOWED IN SUMMER REQUIRE DRAINAGE. Lands overflowed by the regular tides of the ocean require drainage, whether they lie upon the sea-shore, or upon rivers or bays. But this drainage involves embankments, and a peculiar mode of procedure, of which it is not now proposed to treat. Again, all lands overflowed by Summer freshets, as upon rivers and smaller streams, require drainage. These, too, usually require embankments, and excavations of channels or outlets, not within the usual scope of what is termed thorough drainage. For a further answer to the question--what lands require drainage? the reader is referred to the chapters which treat of the effect of drainage upon the soil. SWAMPS AND BOGS REQUIRE DRAINAGE. No argument is necessary to convince rational men that the very extensive tracts of land, which are usually known as swamps and bogs, must, in some way, be relieved of their surplus water, before they can be rendered fit for cultivation. The treatment of this class of wet lands is so different from that applied to what we term upland, that it will be found more convenient to pass the subject by with this allusion, at present, and consider it more systematically under a separate head. ALL HIGH LANDS THAT CONTAIN TOO MUCH WATER AT ANY SEASON, REQUIRE DRAINAGE. Draining has been defined, "The art of rendering land not only so free of moisture as that no superfluous water shall remain in it, but that no water shall remain in it so long as to injure, or even retard the healthy growth of plants required for the use of man and beast."