THE MOON S FACE. 
275 
discriminately mingled, and interference is a common phe¬ 
nomenon. If, as I have assumed, the moonlets approached 
the moon approximately in the plane of its equator, the fact 
is not attested by the grouping of the craters in a medial 
zone, and so it is necessary to assume further that the axis 
of rotation was not constant. This assumption need occa¬ 
sion no difficulty, for unless the approaching moonlets moved 
precisely in the plane of the moon’s equator, their collisions 
would disturb its axis of rotation, and there is no reason to 
suppose that these disturbances would be compensatory rather 
than cumulative. Under the successive impulses thus given 
the moon’s equator may have occupied successively all parts 
of its surface, without ever departing widely from the plane 
of the moon’s orbit. 
Sculpture .—The rims of certain craters are traversed by 
grooves or furrows, which arrest attention as exceptions to 
the general configuration. In the same neighborhood such 
furrows exhibit parallelism of direction. Similar furrows 
appear on tracts between craters, and are there associated with 
ridges of the same trend, some of which seem to have been 
added to the surface. Elsewhere groups of hills have oval 
forms with smooth contours and parallel axes, closely resem¬ 
bling the glacial deposits known as drumlins, but on a much 
larger scale. Tracing out these sculptured areas and platting 
the trend lines on a chart of the moon, I was soon able to recog¬ 
nize a system in their arrangement, and this led to the detec¬ 
tion of fainter evidences of sculpture in yet other tracts. The 
trend lines converge toward a point near the middle of the 
plain called Mare Imbrium, although none of them enter 
that plain. Associated with the sculpture lines is a peculiar 
softening of the minute surface configuration, as though a 
layer of semi-liquid matter had been overspread, and such I 
believe to be the fact; the deposit has obliterated the smaller 
craters and partially filled some of the larger. These and 
allied facts, taken together, indicate that a collision of ex¬ 
ceptional importance occurred in the Mare Imbrium, and that 
one of its results was the violent dispersion in all directions 
