A COMPARISON OF THE FEATURES OF THE EARTH AND THE MOON. 77 



The form of the so-called mountains demands a careful inquiry. It is 

 asserted that in some cases the steeper slopes, in certain groups of these eleva- 

 tions, are all, or prevailingly, in a particular versant ; this point should be 

 determined. It appears likely that the mountains in different fields vary in shape 

 in a manner which will permit them to be classified according to areas. All such 

 variations are sure to have meaning. As a part of this work, the cones in the 

 center of vulcanoids such as that in Theophilus should be compared with the 

 peaks in the mountain systems. 



I have noted that the older vulcanoids in the central field of the moon's 

 surface appear to have been elongated or " spooned " in a north and south 

 direction, and that this change may be due to the loss of the original rotation of 

 the sphere. This point needs further study. If my observations be verified, 

 and it be found that the newer vulcanoids are not deformed as by a collapse 

 of the equatorial bulge due to the loss of rotation, then the time of the change 

 in relation to the development of the surface features may be determined, and as 

 the loss of rotation would have been very gradual it would be incidentally shown 

 that the period during which vulcanoid processes affected the surface was very 

 extended. 



The phenomena of contact of the maria with their shores needs close study. 

 I have briefly stated the facts which lead me to the opinion that the lavas of 

 these fields originally and for a brief time rose much above their present level 

 and have since withdrawn from low areas they at first flooded over. If this be 

 affirmed, then we have evidence that the order of fluidity of the lavas in question 

 was far higher than that of the vulcanoids, where, as we have seen, the material 

 appears to have been at a low average temperature, or at least very viscid, so 

 that it consolidated on very steep slopes as soon as it escaped from the craters. 

 Much depends on the determination of the relative temperature of these groups 

 of lavas, for if those of the maria were decidedly hotter than those of the vul- 

 canoids hotter, indeed, than any molten material which is known to have come 

 forth from the interior of the moon or the earth, then the presumption that they 

 were due to in-falling bodies is so far affirmed. 



It is most desirable to ascertain the circumstances of contact of the lavas of 

 the several maria which are obviously connected. If they are the result of the 

 impact of one falling body, or of several which fell at about the same time and 

 place, then the various connected areas should be perfectly confluent. If the 

 bodies fell here and there, affording separate centers of melting, then there may 

 be a trace of juncture of the lavas where they joined their floods. My own 

 opinion, based on rather scanty observations, is that the confluence of the appar- 

 ently connected maria is complete, and that their lavas were generated by one 

 incident ; the distinctly separated areas, the Mare Crisium and the Mare Australe 

 as well as the Mare Humboldtianum, if the two last named be, indeed, true 

 maria, having been formed apart from the main field, which includes all the other 

 areas classed in this group. 



The naturalist, trained in interpreting terrestrial phenomena, learns the value 



