1904 - 5 .] Mr Romanes on the Formation of the Moon. 475 
occur outside the crater walls as well as inside; but the writer 
does not find that Professor Shaler accounts for those on the out- 
side. In discussing G. K. Gilbert’s hypothesis, that the craters 
were due to impacts, he rejects it, because, he says in a footnote 
(page 12), the masses or bolides would have struck with velocities 
that would have raised their temperature more than 150,000 
degrees (scale not stated). He (probably after Gilbert) is thinking 
of velocities of 7J miles per second or more. The possibility of 
such masses (bolides) having always been in company with the 
earth and moon has not occurred to him; and he objects (page 12) 
that such impacts would have caused much cracking of the moon’s 
surface — thinking, no doubt, of hard masses striking stone, but 
not considering that the bodies striking might have been more 
like heaps of loose material moving generally with the velocity of 
only 1J mile per second. 
Again, Professor Shaler thinks that the maria must have been 
formed, each by the impact of one or more bolides with planetary 
velocities (page 17), and he considers the great amount of melting 
of rock they could produce ; but he does not sufficiently consider 
that a mass moving at such velocity, instead of melting a great 
quantity of rock, would melt only a moderate quantity, and spend 
much of its energy in driving the melted rock right away from 
the moon in a great splash. 
Professor Shaler has taken an immense amount of care, and 
given many years of labour to accumulate facts as to the moon, 
and he has stated those facts with great impartiality for the 
benefit of science; but in explaining the causes at work in pro- 
ducing them, the writer thinks he has started from w 7 rong 
premises, and found difficulties that disappear when the true 
causes become known. 
The writer will now state his views as to the cause of some of 
the principal lunar formations. He thinks that the circular or 
slightly elliptical craters have been formed by the impacts of bodies 
belonging to the earth’s system, of all sizes up to 20 miles or more 
in diameter. The floors of these craters are in general much 
depressed below the surrounding surface, and the crater walls are 
sometimes of such great elevations as 17,000 feet or more above 
the floors, while the diameter of the craters varies from the 
