94 TRANSATIONS OF THE [FEp. 6: 
impact of bodies colliding with the moon. It differs as to the 
previous history of the incident 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 components 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 system 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 body 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 rock 
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- 
pathian mountain chain as the remnant of a crater rim with a 
radius of 400 miles. 
Certain parts of the surface are observed to be sculptured by 
an agency acting along lines which, for each locality, are nearly 
parallel, Grooves are plowed, crater rims 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 filling 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 of 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 
