54 
The surface of the Moon, orrather of the side we were able to 
see, was broadly divided into two very distinct classes of features: 
large, dark, comparatively smooth, and level patches ; and bright, 
broken, irregular tracts of land. The darker parts were the Maria, so 
called by the old observers, from their supposed resemblance to seas 
and the beds of former cceans. They might be chiefly likened to our 
terrestrial plains, prairies, and steppes ; were often bounded by hilly 
table-lands and extensive mountain chains. Their general appearance 
was diversified with small pits, sometimes considerable craters, and 
frequently long, low, and more or less sinuous banks. A description 
of their other features was given, and peculiarities traced in the 
various examples pointed out onalarge map. Zhe Walled Plains, as 
they were termed at first sight, seemed to resemble gigantic craters ; 
but a closer acquaintance revealed considerable differences, They 
were of large extent, some being 100 miles in diameter, They pre- 
sented the characteristics of upheaval rather than the explosive forces 
which formed true volcanoes. Some large drawings of notable walled 
plains were exhibited, one showing a fine example almost in profile ; 
another giving an idea of an almost vertical view, The Craters, which 
had evidently played so lively and important a part in the for- 
mation of the Lunar surface, were next noticed. In many parts ot the 
Moon they seemed crowded together in almost inextricable confusion, 
the walls of one crater encroaching on and often partially obliterating 
those of another, while, perhaps, in its own turn, it had received 
numerous shocks from smaller explosions, or been riven by deep 
fissures or clefts, The Lunar craters were on a gigantic scale compared 
with ours, many being from 40 to 60 miles in diameter, and their depth 
from summit of rim to bottom of cavity in some cases even exceeded 
three miles, while the height of rim from the surrounding land was 
often 14 miles. The walls of these enormous bowls were sometimes 
split into almost concentric terraces divided by ravines and arranged 
like the seats of an amphitheatre. Several examples were referred to 
on the map, and a fine drawing of Copernicus, executed by Mr, 
W. W. Mitchell, was much appreciated, 
An interesting account of Mr. W. R. Birt’s discovery of a second 
cone in Tycho was next given 
The Mountain Ranges graduated in all possible diversities of form. 
Continuous Andes-like chains of great altitude sloping in long gradients 
on the one side, and on the other presenting perpendicular cliffs quite 
