9 J: TKANSATIONS OF THE [FeB. 6 



impact of bodies colliding -witla tlie moou. It differs as to the 

 previous bistort' of the iucident bodies. It postulates as the 

 antecedent of the moon an annulus of many small bodies 

 surrounding and revolving about the earth as does the ring of 

 Saturn about that planet. The comi:)onents of this ring after- 

 ward segregated so as to constitute a smaller number of larger 

 bodies, and finally a single body — the moon. The craters of 

 the moon's surface, large and small, are the impact scars of 

 those minor aggregates which were last captured by the 

 moon. 



After the moon had acquired approximately its present mass 

 the velocity of impact for bodies of the s^^stem was about 7700 ft. 

 per second. The energy due to this velocity, if converted into 

 heat, was more than sufficient to fuse the colliding body, assum- 

 ing that bod}"- to have the specific heat and fusing point of 

 diabase. The impacts of small bodies seem to have produced 

 deformation without fusion ; but in the impacts of larger bodies 

 more energy was applied to each unit of surface, and parts of 

 projectile and target were fused, producing the level plains of 

 the larger craters. The recoil of the liquified and softened rook 

 toward the centre produced the central hill characteristic of 

 lunar craters. The corrugated rim of the typical lunar crater is 

 due to outward thrust ; the inward facing cliff overlooking the 

 inner slope, and the broken terraces below it, are due to land 

 slips, a part of the rim falling back into the fused tract. 



The round maria, such as M. Crisium and M. Serenitatis, are 

 regarded as large craters, and the Caucasus-Appenine-Car- 

 jDathian mountain chain as the remnant of a crater rim with a 

 radius of 400 miles. 



Certain parts of the surface are observed to be sculj^tured by 

 an agency acting along lines which, for each locality, are nearly 

 l^arallel. Grooves are plowed, crater riujs are notched, and 

 ridged additions appear to have been made to the surface. The 

 same districts have been flooded by liquid and viscous matter, 

 diminishing the depth of the larger craters, obliterating the 

 small craters, partly tilling cracks (rills), and afterward solidify- 

 ing. In some low-lying districts the more liquid part of this 

 matter collected, producing plains of the second order of 

 magnitude and ever maria. The lines ol sculpture of these 

 districts radiate from a point in the Mare Imbrium. It is 

 believed that the collision of a large moonlet at this place, 

 under circumstances causing much fusion, hurled a deluge of 

 molten and fragmental rock in all directions, flooding and 

 partially remodeling a fourth part of the visible face of the 

 moon. The central tract of the moon lies within the flooded. 



