474 Proceedings of Royal Society of Edinburgh. [sess. 
The writer has been referred to Professor N. S. Shaler’s great 
essay in the Smithsonian Contributions to Knowledge to study his 
views, and to discuss them herein. 
Professor Shaler does not discuss the manner of the moon’s growth 
except by a reference to Professor G. H. Darwin’s theory, a modified 
form of w T hich he apparently accepts (page 3 of his essay), and he 
makes the following assumption on pp. 31-32: “The most 
reasonable view of the interior condition of the moon when its 
vulcanoids (craters) were in activity is that it was in a state of 
essential fluidity with a relatively thin crust.” This is making 
use of a popular idea that the moon, like all other cosmic bodies, 
must at one time have been so hot as to be fluid. This is not a 
scientific view, as no proof of it is possible. Professor Shaler 
makes no attempt to show how the moon became so hot as to be 
fluid, and on page 48, under “ Adjustments of the Surface to Con- 
traction,” he gives the following strong evidence that leads to a con- 
trary inference : “ On the earth he (the geologist) sees in the ample 
folds of the sea-basins and of the continents, as well as in many 
folded mountain chains, what he takes to be evidence of a long- 
continued accommodation of an anciently cooled crust to a central 
mass which is ever losing heat. On the moon he finds what, in 
proportion to the size of that sphere, is surely not the hundredth 
part of such action What then is the meaning of this 
startling diversity in the orogenic history of the two spheres ? ” 
Also on page 4 Professor Shaler states the relative densities of the 
moon and earth as six to ten ; but he does not draw the inference 
that the moon has been less subjected to gravitational compression, 
and therefore has had less internal heating than the earth ; indeed, 
the influence of mass in causing the heating of cosmic bodies 
seems not to have been sufficiently present to his mind. Professor 
Shaler requires the presence of fluid lava a short way below the 
surface of the moon to explain the formation of vulcanoids (craters) 
by a rise and fall of liquid lava through holes in the crust, which 
he supposes have been formed by the help of gases like slow 
boiling ; and he accounts for the formation of terraces on the 
inside of the surrounding walls of the vulcanoids by the different 
levels at which the lava successively stood. These terraces are 
very irregular, and by no means continuously horizontal, and they 
