6o8 FRANCIS PARKER SHEPARD 



the oceans would produce broad plateau-like uplifts rather than 

 closeJy folded mountain ranges. Are such plateau ranges absent 

 on the sea bottom ? Unfortunately soundings of the ocean basins 

 are not very numerous so that there is a tendency to think of the 

 ocean bottoms as being broad flat plains without important relief. 

 However, if we compare sections made across the Atlantic with 

 sections across the United States giving the same number of readings 

 in each case, we find that the sub-oceanic surface has as great major 

 variations in contour as has the land. Figure i represents such a 



BaRTnudaS 



I 



)ooo 



5000 



5 I 



' Mt. M.rchell 



B 



Fig. I. — A comparison of sections with same vertical scale and similar horizontal 

 scale giving the higher points of the Atlantic Ocean and the United States. A, Section 

 of the bottom of the Atlantic Ocean. B, Section across the United States. 



section. The data for the Atlantic ocean was obtained from sound- 

 ings made by the Challenger Expedition.^ Soundings taken 

 recently by a United States destroyer show a more detailed section 

 of the Atlantic,^ which shows still greater irregularities (Fig. 2). 

 Very likely there are great plains on the sea bottom, but these are 

 probably only especially pronounced on the continental platform 

 where recent deposition has evened up irregularities. Plains on the 

 continents are more numerous than hilly surfaces. Such islands as 

 the West and East Indies represent the higher mountain ranges of 

 the ocean bottom. 



If we can grant that there has been important diastrophism on 

 the ocean bottom in the past, then it becomes much more difficult 

 to prove that there has been periodic diastrophism. On the other 



'WyviUe Thompson, "Voyage of the Challenger," the Atlantic, Vol. I, p. 172. 



^ Scientific American, May, 1923, p. 330. 



