White was greatly influenced by Stieglitz’s concept of "equivalence," which White interpreted as allowing photographs to represent more than their subject matter. He wrote "when a photograph functions as an Equivalent, the photograph is at once a record of something in front of the camera and simultaneously a spontaneous symbol. (A 'spontaneous symbol' is one which develops automatically to fill the need of the moment. A photograph of the bark of a tree, for example, may suddenly touch off a corresponding feeling of roughness of character within an individual.)"
While rocks were photographed, the subject of the sequence is not rocks; while symbols seem to appear, they are barely pointers to significance. The meaning appears in the mood they raise in the beholder; and the flow of the sequence eddies in the river of his associations as he passes from picture to picture. The rocks are only the objects upon which the significance is spread like sheets on the ground to dry.
Not everyone agreed with or understood White's philosophy. Some of White's abstract images "have an indeterminacy that forestalls any conventional response."One critic wrote "Without a capacity to see in rocks some glimmer of essential form, as Weston did, or in clouds some hint of a universal life force, as Stieglitz did, one cannot understand White's pictures....One gets the impression that White did not develop as an artist in a linear sense so much as he oscillated between conflicting pole.Wikipedia