FUNDAMENTAL PROBLEMS OF GEOLOGY 267 



bution of thrust and tension. Obviously the rocks of earliest for- 

 mations should show the differential effects of change of rotation 

 most notably, but the Archean formations of high latitudes, where 

 tension should prevail, are crumpled and crushed much the same as 

 in low latitudes, where thrust should prevail. Mountains of all ages 

 are about as abundant north of 33° latitude as in the equatorial 

 belt. Nor are the equatorial mountains notably transverse to the 

 equator, or limited in extent to the demands of the hypothesis. 

 Furthermore, if there had been appreciable change in the form of 

 the earth to accommodate itself to a slower rotation, the water on 

 the surface, being the most mobile element, should have gathered 

 toward the poles, and the less mobile solid earth should have pro- 

 truded about the equator, but the distribution of land and water, 

 present and past, gives no clear evidence of this. The equatorial 

 belt contains a less percentage of land than the area north of it, and 

 more than that south of it. It varies but slightly from the average 

 for the whole globe. 



Geological evidence being thus out of harmonj^ with deductions 

 from the researches of G. H. Darwin on the earth-moon evolution 

 under tidal control, inquiry as to the source of the discrepancy was 

 naturall)' invited. The influence of the ocean tides is probably in- 

 effectual because the varied positions of the derived tides are such 

 as to nearly neutralize their own effects mutually. This conclusion 

 has also been announced recently by Poincare.* The essential ques- 

 tion, therefore, resides in an assumed body tide, and this brings into 

 sharp emphasis the question whether the earth is not either too rigid 

 to give an effective body tide, or so resilient, owing to its high elas- 

 ticity, that the tides do not have the right position to be effective in 

 retardation ; for retardation of rotation is as much dependent on 

 the carrying forward of the tidal protuberance by the earth's rota- 

 tion as on the amount of the protuberance. 



We have endeavored, therefore, to advance the study to include 

 the distribution of rigidity in the earth, as well as its amount, and 

 to recognize the effects of elasticity on the response and the resili- 

 ence of the spheroid to the tidal stresses. Tentative laws of distri- 

 bution of the internal rigidity have been formulated, two of which 

 may serve a temporary purpose until better grounds can be de- 

 veloped. At the present stage of inquiry, it would seem that geo- 



*I,'influence des niarees oceanienes sur la duree du jour est done tout :l fait minime et 

 n'est nullemeut comparable a Teffet des mar6es dues a la viscosite et a I'elasticitS de la partie 

 solide du globe, effet sur lequel M. Darwin a insist6 dans une serie de ni^moires du plus haut 

 iut^rSt. (Bulletin Astronomique, tome XX (June, 1903), p. 223.) 



