Page:Popular Science Monthly Volume 85.djvu/81

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he notes, "two very distinct kinds of structure in the granite of this region ... which determine all the forms about this wonderful valley, ... the concentric structure and a rude, columnar structure, or perpendicular cleavage." By these differentiations he traced the sculpture of every ragged spire or rounded dome. Later, he confirmed his observations by demonstrating the effect of dynamic forces upon the separate formations, showing the processes of sculpturing, whether by quarrying along the least resistant lines of perpendicular Assuring, or the exfoliation of concentric layers of onion-like granite. Coming in close association with John Muir, he accepted his theories of glacial erosion. Following the ancient trough of the grand Tuolumne glacier, he traced its tangential branch which overflowed southward and poured