THE MOON’S FACE. 
243 
be well to place clearly in view the characteristics of the lunar 
craters. The range in size is great, extending from a maxi¬ 
mum of about 800 miles diameter to a minimum of less than 
one mile. The size of the smallest ones is not known, as 
they are beyond the present power of the telescope. Within 
this range are several varieties, more or less correlated with 
size, hut their intergradation is so perfect that they are all 
regarded as phases of a single type.* Those of medium 
size will he first described. 
Picture to yourself a circular plain ten, twenty, fifty, or 
one hundred miles in diameter, surrounded by an acclivity 
which everywhere rises steeply but irregularly to a rude 
Fig. 1.—Type form of lunar crater. 
terrace, above which is a circular clifflikewise facing inward 
toward the plain. This cliff is the inner face of a rugged, 
compound, annular ridge, composed of shorter ridges which 
overlap one another, but all trend concentrically. Seen from 
*The only exceptions.to the type that I have noted are associated with 
certain of the rills. They are so small that I could not determine their 
characters with certaint} r , but they seemed to lack rims and to be hopper¬ 
shaped. 
Neison (op. cit., p. 66) describes “crater cones” as of different type, 
characterized by cups at the apices of cones, but these I did not succeed 
in discovering. On several occasions I saw at the terminator what ap¬ 
peared to be small craters perched on high pedestals, but when the same 
objects were observed at such distance from the terminator as to escape 
the exaggeration peculiar to that illumination, they were seen to be de¬ 
pressed craters of the usual type. 
