326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 31 



and continents as having come into being prior to the present geo- 

 logical age and that our attention should be given to the problem of 

 unfolding the geological record since the beginning of sedimentation. 

 The mind of a human being can not be confined to any particular 

 subject or group of subjects nor to any particular phase of a subject. 

 It is bound to consider any question that presents itself. 



It does seem very strange that we should have great masses of 

 material standing above sea level, as continents and islands, and 

 o;reat troudis or basins below the waters of the oceans. We have 

 enough geodetic evidence to prove conclusively that the ocean bot- 

 toms are depressed because of the greater density of the material in 

 the crust below them, and that the continental and island masses 

 stand above sea level because the density of the material in the crust 

 below them is less than normal ; but what could have caused these 

 abnormal densities ? Why is it that under the continents we have a 

 layer, which some claim is about 20 miles in thickness, of light rocks 

 called granites, while under the oceans we have no granites ? 



There have been many explanations offered as to why we have 

 oceans and continents, but the only one that appeals to me as having 

 decided merit is that advanced by Osmond Fisher. About 40 years 

 ago he wrote a book entitled " Physics of the Earth's Crust," which 

 contains much material of great value. He has a chapter on the 

 possible origin of oceans and continents in which he discusses 

 Darwin's idea that the moon at one time was thrown off from the 

 earth. Darwin's discussion of the birth of the moon was more or less 

 an academic one, and he made no suggestion as to what was the 

 condition of the earth at the time that this birth occurred, but one 

 is led to believe by Darwin's writings that he had in mind a fluid 

 earth. Fisher believed that there was an outer solid shell on the 

 earth at the time that the moon was formed and that the earth lost 

 much of the outer granite shell as a result of the disruption. The 

 places from which the crustal material was thrown off were filled 

 with subcrustal material, but the light granite occupied greater 

 depth than the heavier subcrustal material which replaced it. In 

 consequence the healed scars had surfaces which were lower than the 

 surfaces of the portions of the crustal material which remained. 



Darwin's hypothesis is based on the idea that the earth was ro- 

 tating very rapidly and that as it slowed down to such a rate of 

 rotation as would make the tides, caused by the attraction of the sun, 

 sj'nchronize with the natural period of vibration of the earth, there 

 would be an accumulation of tidal effect which would make the 

 earth's mass unstable. Darwin estimated that at the time of, or 

 just before, the disruption, the major axis of the earth was about 

 twice the length of the minor axis. This would mean that the 



