At this morning's MSL press conference the panel focused on the alluvial fan and evidence suggesting that water once flowed there on Mars. The alluvial fan is similar to those found on Earth. A related press release contains the images from the teleconference and of the layer of conglomerates from Hottah, one of the outcrops that Curiosity passed on her way to Glenelg. The conglomerate consists of small rounded pebbles cemented together which on Earth is associated with a flow of water. The pebbles are the remains of worn down rocks that are too large to be moved by the wind so this seems to imply the presence of something like water as the motive force. On Earth water supplies hydroxides which helps bind gravel and a material like cement together to form cohesive mass. Chemical studies are needed to determine the mechanisms responsible on Mars. Wind blown sand and small skipping stones might gain enough momentum traveling downhill to move about larger stones and wear them down but the current conditions at Gale Crater produce flat faces like that found on Jake Matijevic. Rock tumblers usually employ a lubricant.
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