CONTINUITY. 193 



craters were the result of a single explosion, which raised the 

 surface as a bubble and deposited its debris around the orifice 

 of eruption. 



The eruptions on the surface of the moon clearly did not 

 take place at one period only, for at many parts of the disk cra- 

 ters may be seen encroaching on and disfiguring more ancient 

 ones, sometimes to the extent of three or four successive 

 displacements. Two important questions might, it seems to 

 me, be solved by an attentive examination of such portions 

 of the moon. By observing carefully with the most powerful 

 telescopes the character of the ridges thus successively formed, 

 the successive states of the lunar surface at different epochs 

 might be elucidated ; and, secondly, as on the earth we should 

 look for actual volcanic action at those points where recent 

 eruptions have taken place, so on the moon the more recently 

 active points being ascertained by the successive displace- 

 ment of anterior formations, it is these points which should 

 be examined for existing disruptive disturbances. Metius 

 and Fabricius might be cited as points of this character, 

 having been found by M. Chacornac to present successive 

 displacements, and to be perforated by numerous channels or 

 cavities. M. Chacornac considers that the seas, as they are 

 called, or smoother portions of the lunar surface, have at some 

 time made inroads on anteriorly formed craters ; if so, a large 

 portion of the surface of the moon must have been in a fused, 

 liquid, semi-liquid, or alluvial state long after the solidifying of 

 other portions of it. It would be difficult to suppose that 

 this state was one of igneous fusion, for this could hardly 

 exist over a large part of the surface without melting up the 

 remaining parts ; on the other hand, the total absence of any 

 signs of water, and of any atmosphere, or, if any there be, it is 

 most attenuated, would make it equally difficult to account 

 for a large diluvial formation. 



Some substances, like mercury on this earth, might have 

 remained liquid after others had solidified by the cooling of 

 the planet ; but the problem is one which needs more examina- 

 tion and study before any positive opinion can be pronounced. 



I cannot pass from the subject of lunar physics without 

 recording the obligation we are under to our late President 



O 



