f Mars that Mr. Lowell describes
with much confidence is, that it is wonderfully uniform and level, which
of course it would be if it had once been in a liquid or plastic state,
and not much disturbed since by volcanic or other internal movements.
The result would be that cracks formed by contraction of the hardened
outer crust would be vertical; and, in a generally uniform material at a
very uniform temperature, these cracks would continue almost
indefinitely in straight lines. The hardened and contracting surface
being free to move laterally on account of there being a more heated and
plastic layer below it, the cracks once initiated above would
continually widen at the surface as they penetrated deeper and deeper
into the slightly heated substratum. Now, as basalt begins to soften at
about 1400 deg. F. and the surface of Mars has cooled to at least the
freezing-point--perhaps very much below it--the contraction would be so
great that if the fissures produced were 500 miles apart they might be
three miles wide at the surface, and, if only 100 miles apart, then
about two-thirds of a mile wide.[15] But as the production of the
fissures might have occupied perhaps millions of years, a considerable
amount of atmospheric denudation would result, however slowly it acted.
Expansion and contraction would wear away the edges and sides of the
fissures, fill up many of them with the debris, and widen them at the
surfaces to perhaps double their original size.[16]

[Footnote 15: The coefficient of contraction of basalt is 0.000006 for
1 deg. F., which would lead to the results given here.]

[Footnote 16: Mr. W.H. Pickering observed clouds on Mars 15 miles high;
these are the 'projections' seen on the terminator when the planet is
partially illuminated. They were at first thought to be mountains; but
during the opposition of 1894, more than 400 of them were seen at
Flagstaff during nine months' observation. Usually they are of rare
occurrence. They are seen to change in form and position from day to
day, and Mr. Lowell is strongly of opinion that they are dust-storms,
not what we term clouds. They were mostly about 13 miles high,
indicating considerable aerial disturbance on the planet, and therefore
capable of producing proportional surface denudation.]

_Suggested Explanation of the 'Oases.'_

The numerous round dots seen upon the 'canals,' and especially at points
from which several canals radiate and where they intersect--t