Abstract
D. Johnson deduced a theory on the forrn.ation of rock fans in arid regions from the principle of planation by G. K. Gilbert. But in his deduction the action of weathering and rain wash was neglected, and the existence of rock fans does not seem to be proved by his. examples.
As the transverse profiles of rock floors in Central. Korea are gently rolling and thinly covered by gravel beds, they appear to be rock fans. But they are terminal parts of gently declined spurs, of which flanks are graded to the local baselevels of neighbouring valley floors by weathering and rain wash.
Therefore, the author put a doubt upon deduction by Johnson, thought to be necessary to reexamine examples, showed by him and put a tentative hypothesis on the formation of rock floors similar to rock fans.
