The Ocean 



19 



ocean bottom, based on a few wire soundings, gave rise earlier to an impression of a 

 certain smoothness and evenness of the sea bottom. Especially the bottom slope 

 between two sounding points was ascertained and in most cases was found to be 

 less than the smallest deviation from horizontal that the human eye can still detect, 

 (a slope of 1 : 200 or a slope angle of 0° 17'). Actually, values found in this way showed 

 very few vertical divisions over wide stretches of the ocean. This very smooth sea- 

 bottom topography has, however, been shown by the much closer values given by 

 echo sounding to be at least partly a misapprehension caused by the small number of 

 wire soundings. Without doubt the sea bottom on the whole and especially away from 

 areas where orogenetic and volcanic forces are active is on a small scale far more 

 smooth and even than the surface of the land. The effects of the atmosphere, weather- 

 ing and erosion by running water which all contribute to the variety of small forms 

 which occur on land surfaces are of course all absent. However, echo-sounding pro- 

 files at close intervals very often show considerable bottom irregularity. All echo- 

 sounding profiles so far obtained are similar in this respect. The morphological inter- 

 pretation must be made with the greatest caution since for greater clarity the results 

 are usually shown with a strongly exaggerated vertical scale. Some vertical distortion 

 is, however, essential when the profile extends over such great distances in order to 

 show the details of the sea bottom clearly. Figures 1 1 and 12 show the "Meteor" profile 



Echolot of "meteor" on profile 5K 



5000 



Fig. 1 1 . Echo sounding profile across the South Atlantic obtained by the "Meteor" at 23 "^ S. 

 (profile VII: 21-25-24° S.); with 180-fold enlargement of the vertical scale and disregarding 



the curvature of the Earth. 



Fig. 12. The same echo sounding profile as in Fig. 11 taking the curvature of the Earth into 

 account. Upper curve: vertical enlargement 1:3; lower curve: 1:30 (according to Stocks). 



VII (21-25-24° S.) in two different forms (according to Stocks, 1936). The upper 

 diagram shows the echo-sounding profile along a line from Rio de Janeiro to Whalefish 

 Bay with a 180-fold magnification of the vertical scale and without taking the curva- 

 ture of the Earth into consideration. In the lower profile, on the same horizontal 

 scale, the curvature of the Earth at latitude 23° has been taken into account; the outer 

 arc is the surface of the sea, and below this the upper curve shows the sea bottom with 

 a vertical exaggeration of 3 : 1 while the lower curve shows the sea bottom with a 

 vertical exaggeration of 1 : 30. The details of bottom topography and changes of 

 slope are still easily recognizable on the curve with a 30-fold vertical exaggeration and 



