A COMPARISON OF THE FEATURES OF THE EARTH AND THE xMUUX. I9 



would bring about the consequences we note. At least one such mass of 

 matter, Eros, apparently not to be classed either with planets or satellites, has 

 recently been discovered at no great distance from the earth. It is possible 

 that in the relatively ancient state of the solar system, when the surface of the 

 moon acquired its crust, these detached masses of matter were more abundant 

 than they are at present. The tendency would be for those near the greater 

 spheres to be drawn in upon them, with the result that they would become 

 rarer near the planets and the larger satellites. 



As for the origin of detached bodies of the bolide type, we have no basis 

 for more than conjecture ; we may, however, fairly suppose that the explosive 

 action, which is of not infrequent occurrence in the fixed stars, may have hap- 

 pened in the case of our sun or even of the planets, with the result that masses 

 of matter, perhaps originally gaseous or possibly in the molten state, were flung 

 so far away that they acquired independent orbits. 



Although the direct evidence going to prove that the maria are the result of 

 the in-falling of large meteoric bodies is not complete, the hypothesis appears to 

 me to have distinct value for the reason that the cause is sufficient to produce 

 that evidently sudden development of large bodies of very fluid matter, which, 

 for reasons before given, cannot fairly be supposed to have come from the in- 

 terior of the lunar sphere. It is, in a word, the only working hypothesis that I 

 have been able to find which in any way serves to explain these remarkable 

 features of the lunar surface. 



In considering the details of the maria it is to be noted that it is not neces- 

 sary to account for all of them by supposing a single falling body brought about 

 the melting. In several instances, especially in the case of the Mare Australis, 

 and sundry other indistinct patches of the mare quality, the hypothesis can best 

 be applied by assuming that a number of such bodies fell at about the same time 

 and relatively near together. In this way we can account for the fact that in 

 place of normal, rudely circular fields of melting, as in the case of the M. Crisium, 

 we find an irregular, somewhat ragged field of this nature ; in some instances 

 with a periphery that suggests that there were several centers of dispersion of 

 the fluid. Gilbert has maintained that the connected seas were formed by the 

 in-falling of a mass upon the region occupied by the M. Imbrium. This view 

 seems to me to be contradicted by the fact that in the passages between the 

 connected maria there is no evidence of scouring action such as would have been 

 brought about by the swift movement of great masses of lava. 



tt may also be said that the evidence of melting down of the pre-existent 

 topography on the margin of the maria varies much. It appears most clearly in 

 the c'lse of the large, distinctly circular field of the Mare Crisium, and is least in- 

 dicated in the irregular areas. Such are the conditions we should expect to find 

 broucrht about by the fairly supposable variations in the size and number of the 

 masses in any one fall. Thus, so far as my examination of the problem has 

 gone, the supposition that the maria have been formed by sudden melting of col- 

 liding bodies and of the lunar surface about the point of collision appears to be 



