The origin of folded mountains is by most investigators considered as a problem of tectonics; according to my view, however, the orogenesis is as much a problem of regional metamorphism and granitisation. The intimate connection between folded mountain chains on the one hand and dynamothermal metamorphism and granitisation on the other hand has made me try to work out a new theory pertaining to some questions concerning the origin of folded mountain chains. In the following few pages the principal feature of the theory is discussed.