262 W. B. Taylor — Crumpling of the Earth's Crust. 



those circles ; while the equatorial tides — during the equinoc- 

 tial periods — occur when the sun (and the mean lunar plane) 

 have their most rapid change of declination. If it be said 

 that a tidal elevation of two or three feet is too utterly insig- 

 nificant a space, and a cycle of half a year too utterly insig- 

 nificant a time to affect the vast erections of secular progression, 

 the reply is that this minute relaxation of particular zones — 

 unceasingly repeated and continued — may well facilitate the 

 slow but gathering movements of the crust from its strong- 

 compression, and may even to some extent give direction to 

 their energies. As a concurrent though perhaps unimportant 

 circumstance, the fact may be mentioned that while the north- 

 ern tropic encounters 35 per cent of dry land, and the southern 

 tropic nearly 25 per cent, the equator embraces but 21 per 

 cent of land. 



George Darwin, discussing the differences of tidal energy 

 and lagging at different latitudes (in a viscous spheroid), by 

 reason of which the retarding influence is greatest at the equa- 

 torial zone, suggests the possibility of this tendency causing a 

 westward drift of mountain folds and continents in the lower 

 latitudes (as compared with polar regions) and remarks : 

 " There can be little doubt that on the whole, the highest 

 mountains are equatorial, and that the general trend of the 

 great continents is north and south in those regions. The 

 theoretical directions of coast line are not so well marked in 

 parts removed from the equator."* Here again, the striking 

 significance of this physiographic generalization appears to be 

 strangely overlooked. 



It has been an occasion of some surprise that in all the geo- 

 logical literature to which I have had access, I have been able 

 to find but a single allusion to the hypothesis here advanced 

 in explanation of the palpable tangential compression of the 

 earth's exterior strata. 



This one allusion is given in Mr. O. Fisher's interesting 

 work on the "Physics of the Earth's Crust," and is by him 

 referred to, only to be dismissed in a brief paragraph. His 

 reference is as follows : " The friction of the tides — whether 

 oceanic or bodily — must necessarily have diminished the rota- 

 tional velocity, and lessened the oblateness. The parts of the 

 crust about the poles will consequently have been subjected to 

 stretching, and those about the equator to compression. There 

 is however no apparent reason immediately to connect the in- 

 equalities with this cause, for the continents do not occupy an 

 equatorial belt — as they would do under this hypothesis, nor 

 have the polar regions been free from the compression which 

 all continental areas have experienced."! 



* Phil. Trans. Roy. Soc, Dec. 19, 1878, vol. clxx, p. 589. 



f Physics of the Earth's Crust, 8vo, Lond., 1881, chap, xiv, p. 183. 



