This assumption is absolutely essential to support the other great assumption, that the wonderful network of perfectly straight lines over nearly the whole surface of the planet are irrigation canals.

It is not alleged that irregularities or undulations of a few hundreds or even one or two thousands of feet could possibly be detected, while certainly all we know of planetary formation or structure point strongly towards _some_ inequalities of surface.

Mr.
Lowell admits that the dark portions of the surface, when examined on the terminator (the margin of the illuminated portion), do _look_ like hollows and _may be_ the beds of dried-up seas; yet the supposed canals run across these old sea-beds in perfect straight lines just as they do across the many thousand miles of what are admitted to be deserts--which he describes in these forcible terms: "Pitiless as our deserts are, they are but faint forecasts of the state of things existent on Mars at the present time." It appears, then, that Mr.Lowell has to face this dilemma--_Only if the whole surface of Mars is an almost perfect level could the enormous network of straight canals, each from hundreds to thousands of miles long, have been possibly constructed by intelligent beings for purposes of irrigation; but, if a complete and universal level surface exists no such system would be necessary._ For on a level surface--or on a surface slightly inclined from the poles towards the equator, which would be advantageous in either case--the melting water would of itself spread over the ground and naturally irrigate as much of the surface as it was possible for it to reach.

If the surface were not level, but consisted of slight elevations and expressions to the extent of a few scores or a few hundreds of feet, then there would be no possible advantage in cutting straight troughs through these elevations in various directions with water flowing at the bottom of them.

In neither case, and in hardly any conceivable case, could these perfectly straight canals, cutting across each other in every direction and at very varying angles, be of any use, or be the work of an intelligent race, if any such race could possibly have been developed under the adverse conditions which exist in Mars.
_The Scanty Water-supply._ But further, if there were any superfluity of water derived from the melting snow beyond what was sufficient to moisten the hollows indicated by the darker portions of the surface, which at the time the water reaches them acquire a green tint (a superfluity under the circumstances highly improbable), that superfluity could be best utilised by widening, however little, the borders to which natural overflow had carried it.
Any attempt to make that scanty surplus, by means of overflowing canals, travel across the equator into the opposite hemisphere, through such a terrible desert region and exposed to such a cloudless sky as Mr.Lowell describes, would be the work of a body of madmen rather than of intelligent beings.