The western floor of the lunar formation Schickard

The highly complex structure of this region of the lunar surface appears to be due to a combination of extensive fissuring, rifting, primary impact cratering, secondary impact cratering and the flooding of large areas with basaltic lava. The modification of part of the floor of Schickard by early secondary impact cratering has been attributed to the massive expulsion of ejecta from the very large Mare Orientale event. However the current distribution of both major and minor features, and their resulting structures, suggests a more complicated history. Furthermore the initial Orientale impact could have resulted in extensive radial and concentric faulting, central to the point of impact, as well as the massive expulsion of ejecta. Underlying fissuring could have pre-determined the locations for later eruptions by low viscosity basalts, giving rise to areas of flooding and feature obliteration. Also some explanation is needed to account for the marked polygonal structure of certain crater walls (e.g. Schickard M). Using techniques described previously in the Journal, photo-mosaics and detailed drawings have been prepared from the Schickard Orbiter IV HR160/2A microfilm frame, using low power photomicrography and microscopy with a Nikon microscope.