AS15-2611(M)

Figure 185

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This south looking oblique view, centered near 25.5° N, 50.5° W, depicts a prominent "cobra head" rille, Vallis Schroteri (Schroter's Valley). In the foreground is the Aristarchus plateau, and in the background the smooth surface of Oceanus Procellarum. The two large craters in the middleground are Aristarchus (38 km diameter) on the left, and Herodotus (30 km diameter) on the right. At first look the sinuous, flat floored Schroter's Valley and the tightly meandering channel within bear a striking resemblance to river valleys on Earth, and some viewers of the Moon have thought that sinuous rilles were formed by flowing water. In detail, however, sinuous rilles differ from river valleys in many respects; for instance, Schroter's Valley becomes smaller toward its downstream end. They are much like an entirely different terrestrial feature-lava channels. (See fig.  189.) Most geologists think that Schroter's Valley is a channel through which lava flowed from the circular crater at the "head" of the rille to the lower elevation of Oceanus Procellarum, a distance of  approximately 175 km. Figures  186  to  188  are enlargements of the four sided areas outlined in this photograph.   -M.C.M.