Differential erosion and equiplanation in portions of Yukon and Alaska

A study of the physiography of any district involves not only a con sideration of the surface phenomena, but an examination of the ma terials composing that portion of the earth's crust and an investigation of the subterranean forces to which they have been subjected.A steeply inclined valley wall may merely indicate a youthful period in the topo graphic cycle; may be the result of glaciation; may be due to some in herent bedrock structure or the inclination of certain strata, or may even have been caused by recent faulting.In investigating any physiographic problem, therefore, all the avail able evidence which tends to elucidate the physiography should be con sidered, no matter how superficial or deep seated may be the materials or forces involved.I t is thus that the domains of physiography and general geology encroach and overlap-but always to their mutual ad Notes America