128 THE BORDERLAND OF SCIENCE. 



Indeed, we can have no doubt that Mars has been the 

 scene of those volcanic disturbances to which our own 

 mountains, hills, valleys, and ravines owe their origin. 

 The very existence of continents and oceans implies an 

 unevenness of surface which can only be explained as 

 the effect of subterranean forces. Volcanoes must exist, 

 then, in Mars ; nor can his inhabitants be wholly safe 

 from such earthquake throes as we experience. It may 

 be questioned, indeed, whether subterranean forces in 

 Mars are not relatively far more intense than in our 

 own earth, the materials of which the planet is formed 

 being not only somewhat less massive in themselves, 

 but also held down by a gravity much less effective. 



It would seem, also, that the Martial oceans must be 

 traversed by currents somewhat resembling those which 

 traverse our own oceans. There is, indeed, a very 

 marked difference between our seas and those of Mars. 

 For apart from the circumstance that the terrestrial 

 oceans cover a much greater proportion of the earth's 

 surface, the Martial seas are scarcely traversed by ap- 

 preciable tides. Mars has no moon to sway his ocean 

 waters, and though the sun has power over his seas to 

 some slight extent, yet the tidal waves thus raised 

 would be very unimportant, even though the seas of 

 Mars were extensive enough for the generation of true 

 tidal oscillations. For, in the first place, Mars is much 

 farther from the sun, and the sun's action is corres- 

 pondingly reduced it is reduced, in fact, on this 

 account alone more than threefold. But further, Mars 

 is much smaller than the earth, and the dimensions of 



