Peculiar concentric structures, here termed gas rings, occur locally in the sandy, gypsiferous, bentonitic clay of Rich playa on the Llano Estacado. Although only 30 structures were found, onthe surface or in shallow water, cross sectioning of the playa shoreline indicates preservation of earlier structures by filling of the low, troughlike areas. The most probable origin is by escape of entrapped gas (type unknown). These structures are significantly different from gas pits described by Maxon (1940).

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