280 
GILBERT. 
to a molehill—I believe that this resemblance is more than 
accidental, and that the lunar furrows were really formed 
b}^ the forceful movement of a hard body ; but the graving 
tool in this case, instead of being slowly pushed forward by 
a matrix of ice, moved with high velocity and was controlled 
only by its own inertia. It was my first idea that the 
furrows are the tracks left by solid moonlets whose orbits at 
the instant of collision were nearly tangent to the surface of 
the moon, and for some of them I have still no better ex¬ 
planation to suggest; but when they came to be platted on 
a chart of the moon’s face it was found that more than half 
of them accord in direction with the trend lines of the 
Imbrian outrush, a relation which can be seen in Fig. 14, 
where they are represented by heavy lines. It thus appears 
possible, if not probable, that they were produced simultane¬ 
ously with the Imbrian deluge, and the implication of power 
is thereby rendered even more impressive. What must have 
been the violence of a collision whose scattered fragments, 
after a trajectory of more than a thousand miles, scored 
valleys comparable in magnitude with the Grand Canyon of 
the Colorado! 
So far as I am aware, but four of these furrows have been 
previously recorded, and only two are well known, the valley 
near Rheita and the valley of the Alps, and I therefore invite 
the attention of observers to the localities indicated by the 
following descriptions. Beer and Madler, who set forth the 
character of the Rheita valley at length and with great clear¬ 
ness, state that it is 187 miles long and from 10 to 25 miles 
broad and has a maximum depth of more than 11,000 feet.* 
Its general course runs from the eastern tangent of the crater 
Rheita southwestward to the northern margin of the crater 
Rheita d. Not far from its southwestern extremity starts a 
smaller valley with a somewhat more southerly course. 
Parallel to this latter valley and somewhat to the southeast 
are a number of minor grooves which give a striated appear- 
* Der Mond, page 389. 
