Figure 145

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Outcrops of layered rock are strikingly evident in the upper part of the far wall of the crater Bessel (17- km diameter) in south-central Mare Serenitatis. The outcrop is most evident where it forms shadows; however, the dark debris that streams downslope from the layered rock is visible even on parts of the crater wall where the Sun has washed out all details of relief. The outcrop is at a uniform distance below the crater rim, indicating that the strata are horizontal. Thus, Bessel furnishes convincing evidence that mare surfaces are underlain by dark layered rock. The dark rock is now known to be basalt that accumulated as successive flows or layers of lava. Bessel is youthful enough that boulders are abundant on its rim and floor. An anomalously high number of boulders is visible in and around the 750-m diameter crater (arrow) on the floor.   -M.C.M.

This web page was created by Francis Ridge for The Lunascan Project
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