290 
GILBERT. 
were hard but rare, liquefaction was a local and temporary 
surface phenomenon, but the general temperature of the sur¬ 
face was low. Impact heat, being evolved simultaneously 
in the surface and the subsurface, was dissipated more rap¬ 
idly from the surface, so that there was a subsurface zone of 
relatively high temperature. The zone thus inferred de¬ 
ductively is also inferred inductively from the disparity of 
cavities and rims in the case of large craters (page 260); but, 
on the other hand, there is little evidence of the wrinkling 
which, theoretically, should result from the adjustment of a 
cold crust to a cooling nucleus. The parallel topography 
southeast of Mare Serenitatis is due to sculpture, and not to 
buckling. The Apennine range, sometimes described as a 
wrinkle, is part of a crater rim. The great cliff called Altai 
mountains probably marks a fault, but has not the habit of 
a range lifted by tangential thrust. The only indubitable 
flexures that may be ascribed to crustal adjustment traverse 
the maria, whose smooth floors are admirably adapted to 
their display. They have anticlinal and monoclinal forms, 
but are so gentle of slope that they are seen only near the 
terminator, and can represent but a minute amount of arc 
shortening. It is therefore probable that the final shrinkage 
of nucleus was small, and the antecedent storage of heat cor¬ 
respondingly small. During the whole period of growth the 
body of the moon was cold. 
This sketch of the life of our nearest neighbor has but 
little in common with the accounts of other biographers. 
To her has been ascribed a fiery youth, after the manner 
of the sun, a middle life of dissipation, like Jupiter and 
Saturn, a hardening and wrinkling old age, toward which 
the earth is tending, and, finally, the end of change, death. 
If the record of her scarred face has now been read aright, 
all that remains of the old narrative is its denouement: the 
moon is dead. 
Age of the Moon .—Selenographers are not yet satisfied 
that the condition of the lunar surface is constant, although 
the history of their search for changes is discouraging. If 
