THE MOON’S FACE. 
291 
the moon’s face shall prove absolutely incommunicative of 
modern change, it cannot be expected to reveal the date 
when its expression last was varied; but, strange as it may 
seem, the earth can give a partial answer, for the earth was 
an actor as well as a spectator of the moon’s drama, and the 
record of its participation lies somewhere among the archives 
of its crust. While the moon was growing the relations of 
orbits and attractions were such that any inoonlet which 
narrowly escaped collision with the moon was enormously 
perturbed, acquiring an entirely different orbit about the 
earth. Many must have been so directed as to collide with 
the earth, and the traces of their collision, if ever discovered, 
will tie together at a new point the chronologies of satellite 
and planet. 
The results of collision with the earth may have been 
very different from the lunar phenomena. The energy of 
impact determined by the earth’s attraction was 22 times as 
great as that determined by the moon’s. It would suffice 
to melt a body of diabase 30 times as large as the moon- 
let. The shock was somewhat lessened by the atmospheric 
cushion, but a inoonlet of medium size must have developed 
an immense quantity of heat, and may be imagined to have 
projected molten rock far and wide, just as the white streaks 
were projected over the moon. 
Does the earth exhibit impact craters? If not, then 
erosion and sedimentation have destro}^ed them, and the 
Cenozoic era did not witness the building of the moon. Is 
any horizon of stratified rocks generally or widely charac¬ 
terized by molten disjecta? If not, then the moon was 
already a finished planet* in Paleozoic time. Should both 
questions be answered in the negative, and the lunar event 
thus relegated to the hazy dawn of the geologic day, is it 
then oossible that the earth, by taking tribute from the 
moonlet swarm, introduced into its crust an element of 
heterogeneity, which initiated not only the differentiation 
of continental and oceanic plateaus, but the series of geo¬ 
graphic transformations of which geologic structure is the 
record ? 
