PARALLELISM OF EQUATOR WITH MEDITERRANEAN ZONE 85 



position of our supposed equator and has been bounded north and south 

 by more or less continuous bands of land. It is the u Centrales Mittle- 

 meer " of Neumayr. Indeed, in the Eocene many groups of littoral 

 animals can be followed along the continuous shores of this nummulitic 

 sea from India through the Mediterranean to Panama, and in the Cre- 

 taceous the Rudistse had a similar distribution. We may assume the 

 former greater rotation of the earth with the pole at Bering strait to have 

 stood in causal relation with these bands of land and this continuous 

 belt of water. This is an added argument for the supposed position of 

 the pole. 



5. The Mediterranean zone, with its deep depressions and curved moun- 

 tain chains with volcanoes on the concave sides, finds a possible expla- 

 nation in the assumption that these chains may have slid down or have 

 been thrust down the northern slope of the former greater equatorial 

 protuberance, as it subsided because of the diminishing velocity or be- 

 cause of readjustments dependent on the motion of the pole toward its 

 present position. 



Is such a slope possible? The equatorial sea, described in the last sec- 

 tion, which continued into the Eocene, may be taken as an indication 

 of greater velocity, and thus of greater oblateness. 



Darwin makes the life of the planet begin about 57,000,000 years ago, 

 with a rotation of 5f hours, which in about 10,000,000 years had come to 

 be 151 hours. Plotting his values and continuing the curve to the pres- 

 ent date, we get as maximum values a day of about 19J hours 25,000,000 

 years ago, and 22 \ hours 10,000,000 years ago. Darwin, in discussing 

 the table from which the above values are taken, expresses the opinion 

 that some part of these changes, referring mainly to the numbers men- 

 tioned in the first part of the above statement, could have taken place 

 in geological time.* 



In the article cited above Taylor makes the oblateness when the earth 

 rotated in 6 hours 396 miles greater than at present. 



At the instance of Professor Van Hise, Professor C. S. Slichter f calcu- 

 lated the oblateness of a homogeneous spheroid rotating in 5i hours to 

 be 113 miles, and the surface 210,000 miles greater than at present on 

 that account, and on the assumption of a heterogeneous spheroid and 

 Laplace's law of the relation of density and pressure and a rotation 

 period of 5? hours the " changes of pressure " would in addition cause 

 a minimum increase of surface above the present of 1,700,000 square 

 miles. 



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

 Phil. Trans. Roy. Soc, vol. clxx, part ii, 1S79, pp. 401, 581. 

 t Jour. Geo!., vol. vi, p. GO. 



XII— Bull. Geol. Soc. Am., Vol. 11, 1899 



