The completion of the preliminary geologic mapping of the equatorial belt of the Moon allows a first look at the history of a large piece of the lunar crust. Twenty-eight quadrangles at a scale of 1:1 million, amounting to 3 million square miles, have been mapped, and a compilation at a scale of 1:5 million has been made. Field studies of terrestrial impact and volcanic craters are underway, and laboratory studies of crater formation by hypervelocity impact and impact metamorphism of the rocks are continuing.

The Moon is studied by examination of telescopic and spacecraft photography, by visual telescopic observations, by photometry, by polarization, and by infrared, radar, and microwave radiation.

The geologic development of a large linear basin, first worked out in the Imbrium region on the basis of smaller-crater morphology and deposits, has been amplified and extended. A similar sequence of events is indicated by the deposits around other lunar basins. A preliminary attempt can be made to interrelate the basinal histories. Several areas are blanketed by complex volcanic deposits of several types and several ages. The interlayered volcanic and ejecta deposits are offset by at least four episodes of faulting. The processes affecting the original constructional topography have been worked out in lowland areas and are being applied to the more complex uplands. Sedimentation, erosion, isostatic adjustment, and tectonic deformation gradually obliterate lunar craters. Sediments are formed by impact and volcanic processes, and both may cover large areas.

End_of_Article - Last_Page 626------------