Geology of' the Moon. 280 



small body the refrigeration of the surface should, in general, be more ra- 

 pid, so that the internal spaces which remain free should, in proportion to 

 the agitating forces, be more compressed than in a larger body. 



It is perhaps on this account that the earth presents, in comparison of tlie 

 moon, so few traces of these eruptions. The form of our globe generally is 

 not characterized by them, but by upheavings and precipitations {JieJmngen 

 imd niedenchVdge). These last, again, seem to be entirely wanting in tb > 

 moon. As to upheavings, they appear, at least in gi-eat part, to have given 

 place in our satellite to complete eruptions, the result of which must liave 

 been the more energetic, smce the space travelled over on the moon, as the 

 result of equal eruptive forces, would be 6^ times greater than upon the 

 earth. These effects have occurred neither at the same time, nor in the 

 same external circumstances. The annular mountains, which exhibit the 

 radiated system, would appear to have been the result of the most ancient 

 reactions. The more recent encountering a harder substance had less 

 powerful effects, and the dimensions of the crater ought, therefore, sen- 

 sibly to be less ; the eruption had both a more determinate tract, and 

 occurred at a lower temperature. Besides, all the eruptions were not com- 

 pletely centrical ; there were some which acted linearly under the surface, 

 as the compressed ranges of annular mountains and craters prove, and not 

 less the furrows {riUen)^ of Avhich a considerable number are found upon the 

 moon, although, in general, they are perceived only with difficulty.* 



It would appear that there have also been some subsidences {einsturzungen) 

 ,:t the surface of the moon, nor could it well be otherwise after such great 

 ( ii.anges. The round cavities without an annular moinitain, such as are 

 found in the region of Gaiiricus, as well as the great transverse fissures 

 {querklufte) near to Rheita, and in other parts of the south-west quadrant, as 

 also perhaps the valley of the Alps, may belong to formations of this kind 

 at the surface of the moon, in which eruptions may have had only an indi- 

 rect effect. 



The origin of the central mountains is veiy easily explained wlien they 

 are considered as subsequent fonnations. The surface of tlie moon having 

 l)een violently dislocated (««/<;« ?ocJter«) at the places where the first great 

 eruptions occurred, they remained more liable to now ones ; and when the 

 (^ideavours at eruption were repeated, always somewhat more feebly, the 



* According to this hypothesis, Tycho would belong, in the opinion of Messrs Baer 

 and Madlcr, to one of the earlier formations, and its origin would reach to the 

 time when the surrounding mountains, great and small, had as yet no existence. 

 From this opening, the authors add, as from a point of general eruption, would 

 c>scape from the interior of the moon, the elastic fluids which had been separated 

 since its formation, and which were probably at a very high temperature. In thus 

 acting under the surface they would change its internal structure, and by a pro- 

 cess which v/e cannot now explain, they acquired this faculty of reflecting light ; 

 wliich operation, if named vitrification or oxidation, we will not gainsay, provided 

 no ulterior consequences are deduced from the nomenclature. Perhaps the an- 

 nular mountains and the craters which we still find in the radiated system, were 

 formed in some places at the same epoch. But in the immediate vicinity of 

 Tycho the oflrect was not the same, whether that the heat had previously dimi- 

 nished, or that the immediate neighbourhood of the opening enfeebled the ener- 

 gy of the action in some other way. 



