730 PROCEEDINGS OF THE AMERICAN ACADEMY. 



actions, may be in fact impact craters. This idea was put forward by 

 Proctor in 1873 and further enforced by Gilbert some fifteen years or 

 more ago. If they are volcanic then the comparatively diminutive 

 moon has been the theatre of tremendous volcanic disturbances, which 

 without water or other gases and vapors would be unlikely according 

 to the views of some authorities on volcanic action on the earth. If the 

 lunar craters are not volcanic, then the scarred face of our moon is a 

 record of terrific impacts of bodies of all sizes, probably occurring dur- 

 ing its early history millions if not billions of years ago. The earth 

 must also have shared in this bombardment, the traces of which are 

 entirely obliterated. Perhaps its surface was at that time molten. 

 There are marked differences between the now existing volcanic craters 

 on the earth and the lunar craters. On the moon they do not exist 

 along any lines of weakness as on the earth, and they have not built 

 up chains of cinder cones topped by craters of restricted dimensions. 

 They occur on the moon belter skelter, alongside of each other, any- 

 where, everywhere over its much scarred surface. They exhibit the 

 greatest range of sizes or diameters from the smallest dots visible by 

 our most powerful telescopes to the huge basins such as Clavius nearly 

 150 miles across. Large craters are dotted with others, smaller in size, 

 anywhere, it may be on the floor of the crater or in its walls or their 

 slopes. These parasitic craters appear to be absent in such craters as 

 Tycho and Copernicus, which, however, with some others, are distin- 

 guished by extensive systems of whitish streaks running for hundreds 

 of miles in a general direction radially over all irregularities of sur- 

 face. Unlike the earth's great volcanoes, the floor of the lunar craters 

 is in nearly all cases considerably below the general level of the sur- 

 rounding surface. 



The Meteor Crater in Arizona has this same characteristic and in 

 fact if looked down upon from above would appear like a lunar crater 

 transplanted to earth. The proportional depression of the crater floor 

 to the height of the upcast rim is much the same. The outer slope of 

 the rim and its relative extent are likewise very similar. The agree- 

 ment is, to say the least, highly suggestive of a similarity of origin. 

 The lunar craters do not show great rivers of lava coursing down the 

 slopes and covering the lower levels. There is indeed a notable ab- 

 sence on the moon of such evidences. Those whitish streaks around 

 Tycho and Copernicus, bear far more the appearance of an instanta- 

 neous scattering of material in a vacuum (and therefore moving out- 

 wardly in a straight course) than they do of product of a prolonged 

 volcanic eruption which in the case of such large craters must have 

 lasted for years. Any such surrounding deposits would have been 



