CONTINKNTAL I'KOl'.LEMS OF GEOLOfiY. 1(10 



siiniod by tlio (•()ini)I('iii('iit;iiy i);irt of tlio oiaiige \)QqI, wliicli lepresciits, 

 of course, (lint ])ortioii of the occmu outside the (•(^iitiiuMital shoals. In 

 each dia^iain the positions of the i><)les north and south aie rei)re- 

 sented by the letters X and S, From the study of these tigures, and 

 es])ecially from tlieii' sttuly as <Ielineated on the globe, it a]»i)eared pos- 

 sible that a portion of the continental plateau might belt the earth as 

 a great circle. The discovery of such a belt would be imi)ortant, for by 

 assuming that it Avas originally etjuatorial Ave might be led to new hy- 

 p(^theses of continental development. In a rotating liquid si)here the 

 only differentiation of surface condition we can readily conceive is that 

 between equatorial and polar regitms, and if such differentiation were 

 sulticient to cause or localize continental elevations, then these eleva- 

 tions would constitute either t\A'o polar tracts or else an equatorial belt. 

 Moreover, I have been induced by recent studies of the physical history 

 of the moon to suspect that thc^, earth may at one time have received 

 considerable accessions from without and that these accessions were 

 made to the equatorial tract. If these suspicions are well foiiuded, pe- 

 culiar characters may have been given to a tract having the form of a 

 belt. So for a double reason I was led to compare the outline of the 

 continental plateau with a great circle. To this end a great circle was 

 chosen, coinciding as nearly as possible with the line of greatest con- 

 tinental extension, and the projection was so modified as to render the 



ridl'KE 5, — Area vf eontincntdl plateau, dm-loped vith ri'/crcnce to a (ircat circle. 



locus of that great circle a straight line. The result a|)])eais in Figure 

 T), where the stiaight line is tiie ]>ro)ection of the hypothetic ancient 

 e(iiiator; and you will i)robab]y agree with me that it gives little sup- 

 port to the suggestion that the ]>rinci|)al line of contiiuMital elevation 

 was originally eipiatorial. 



Wlnj (Jo eontlnciitdl <irr<(>< r/.sr and Jail f — A foui'lh ])robIem refers to 

 continentaloscillations. Tiiegeologic history ofevery <listrictoftheland 

 includes alternate submergence under and emergence from the sea. 

 To what extent are these changes due, on one hand, to movements of 

 the sea and, on the other, to movements of the land, ;nid what are their 

 (rauses? AVith American geologists the idea, recently advocated, that 

 the chief movements are those of the ocean finds little favor, because 

 some of the most inqxtrtant of the changes ol" which we are directly 

 cognizant are manifestly dilfercntial. Our ])aheozoic maj) ])ictures a 

 sea where now are Ai»i)ala(iiiau uplands and uplands where now are 



