A COMPARISON OF THE FEATURES OF THE EARTH AND THE MOON. 79 



canoid of large size with rather low walls. If it should be proved that these 

 so-called maria do not belong in that clearly-defined group of features, there will 

 be some reason, from their distribution, for believing that they are limited to the 

 hither side of the sphere. 



There are many other lines of work beside that of simple delineation, to 

 which selenographers have so generally confined themselves, which may well 

 engage the attention of those who desire to advance the theory of our satellite. 

 Some of these have been suggested in this memoir ; others will present them- 

 selves in the course of further inquiry. In such work it should be borne in mind 

 that, relatively few and simple as are the forces which have acted on the moon, in 

 comparison with those which have shaped the earth, they are, in their effects, 

 very complex. The variety of objects on that surface is very much greater than 

 the existing accounts of them would lead the novice to suppose. It is only as 

 they are compared after the manner of the naturalist that we may hope clearly to 

 read the wonderful record of that marvelous dead sphere. 



