280 ANNUAL EEPOPvT SMITHSONIAN INSTITUTION, 1928 



development that he finds necessary to fit our determined geologic 

 chronology, on the one hand, and the known development and dis- 

 tribution of ancient faunas, on the other. He realizes that this plan, 

 as well a,s that of Wegener, presents at least one difficulty for which 

 no solution is yet in sight — namely, the breaking down of the land 

 bridges between continents and of the many borderlands, but he is 

 confident that the geophysicists will in time find the way in which 

 this was accomplished. In any event, it seems less insurmountable 

 than the many inaccuracies and " imaginings " that .stand against 

 the tlieory of Pangaea. 



Cosmic time, the writer believes, closed with a molten and layered 

 earth that gave rise, not necessarily to a universal granitic crust 

 (sialsphere), but either (1) to a localized and variably thick one, 

 covering far wider areas than those of the present continents, or 

 (2) to a universal one, very thin over what are now the Pacific and 

 Antarctic oceans; what there was of a granitic shell over these des- 

 tined oceanic areas was " swallowed and digested " by the basaltic 

 substratum or simasphere during the Archeozoic. Over this cold 

 crust of sial and sima may have lain a universal ocean but with 

 probably not more than half the amount of water now on the face 

 of tlie earth; the rest came during geological time. The granitic 

 skin in the places of it,s occurrence was thinner than it is now, and 

 the basaltic substratum, largely glassy, was therefore very mobile 

 because of the greatly heated condition of the interior earth. Geo- 

 logical time had just begun with the dawning of the Archeozoic 

 era, and about one thousand five hundred million years of geological 

 history lie between us and this beginning of earth record in the 

 rocks. 



Archeozoic time Avas one of greatest crustal unrest, for every- 

 where the thin and localized sialsphere was being domed into short 

 mountain ranges, locally folded, compressed, and thrust over one 

 another, and through the deep wounds of fracture rose fluid granite 

 and over the surface vast lava flows. The sialsphere, then an island 

 world, was being crowded and welded together into greater and 

 greater continental islands, between which lay seas, and with seas, 

 rain, and air came into full play the jDhenomena of erosion and sedi- 

 mentation. This topographicallj^ and geographically kaleidoscopic 

 era may have endured during one-third of geological history. 



Proterozoic time was another era of marked sial shifting that 

 lasted through the greater part of another quarter of geologic his- 

 tory. But long before the close of this era the sialsphere appears to 

 have been welded into three zones of transverse or latitudinal lands 

 of great extent, namely, Holarctis, Antarctis, and Equatoris (fig. 4). 

 The latter embraced South America, a land bridge across the present 

 mid-Atlantic, Africa, Madagascar, and Lemuris, including India. 



