2l8 THE BORDERLAND OF SCIENCE. 



rained upon by liquid meteoric masses many tons or 

 even many hundreds of tons in weight, then something 

 like the observed appearance would probably have 

 resulted. Indeed, it is rather a strange circumstance 

 that a fragment of a slab of green shale, pictured in 

 Lyell's Geology, with casts of rain-prints left by a 

 shower which fell ages on ages since, presents as true a 

 picture of certain lunar tracts as a model cast 

 expressly to illustrate what is seen in an actual photo^ 

 graph (moon-painted) of one of those regions. What- 

 ever opinion may be formed as to the significance of 

 this fact, it is certain that the present aspect of the 

 crater-covered regions is quite inconsistent with the 

 idea that there was a single continuous era of 

 crater formation. It is manifest that the contour of 

 the whole surface has been changed over and over 

 again by the forces which produced these craters. 



Although we find little in the moon's aspect which 

 reminds us of features at present presented by the surface 

 of the earth, we must not too confidently assume that 

 the two globes have been exposed to quite dissimilar 

 processes of change. It is very difficult, indeed, to form 

 clear ideas as to the real conformation of the earth's 

 crust underneath those layers which have been formed, 

 directly or indirectly, by the action of air and water. 

 It requires but a slight study of geology to recognise 

 how importantly such action has affected our earth. 

 Indeed, there is not a square foot of the earth's surface 

 which does not owe its present configuration either 

 directly to weather changes and the action of water in 



