RELATIONS OF ROCK FLOW AGE AND MOUNTAIN MAKING. 931 



If Darwin and Peirce are correct in thinking that the moon was once 

 very close to the earth, and that at this early time the earth had a much 

 briefer rotation period than at present, the tidal force tending to produce 

 such monoclinal structures in the zone of flow would be vastly greater than 

 at present. It is worthy of note that the jjreponderant easterly structures 

 which have been noted are among the Paleozoic and pre-Paleozoic rocks 

 which in post-Paleozoic time have been brought to the surface in conse- 

 quence of denudation. If more extended and closer geological studies of 

 cleavage and monoclinal folding lead to the conclusion that easterly 

 structures do preponderate over westerly structures for the earth as a whole, 

 it may be plausibly argued that these phenomena in the old rocks are 

 geological evidence of the correctness of Darwin's general theory in refer- 

 ence to the earth-moon couple, and that the tidal forces in the past were 

 vastly greater than those which now exist. 



I am aware that the foregoing pages upon the relations of rock flowage 

 to mountain making are speculative, but the speculations accord, so far 

 as I know, with the facts of the field. They are here published in the 

 hope that they may lead to more accurate observations ■ of the relations 

 of primary and secondary structures to each other, and of the positions of 

 secondary structures in various mountain regions. Concerning these points 

 I have found the published literature upon the metamorphic rocks woefully 

 lacking. 



o Darwin, G. H., On the precession of a viscous spheroid and on the remote history of the earth: 

 Philos. Trans. Royal Soc, vol. 170, pt. 2, 1879, pp. 530-538. 



