differences in level over wide areas, a circumstance not without practical importance for the laying of cables. For example, out of the 100 soundings carried out for the cable between Midway Island and Guam along a length of 1540 km., the extreme values (5510 and 6277) only differed by 767 m. On a portion 10 geographical miles long, where an average of 14 soundings gave 5938 m., the greatest deviations were + 36 and − 38 m.[1]
It is true that the principle of the smoothness of the ocean floor has recently become somewhat qualified, for it is seen that the network of soundings is too widely meshed to permit of such conclusions, and that an erroneous impression of great levelness can be obtained on land by similarly dispersed separate measurements of altitude. But, with Krümmel, most workers have returned from the temporary exaggerated scepticism to the view that, leaving aside the oceanic troughs, a fundamental difference exists between land and deep sea, although on account of the loss of gravity under water the slopes could be much steeper there than in the air. In this greater smoothness is manifested a greater plasticity, a higher degree of mobility of the floors of the oceans.
Another deduction from this levelness is the absence of folded chains at the bottom of the sea. Whilst the
- ↑ O. Krümmel, Handb. d. Ozeanographie, 1, p. 91. Stuttgart, 1907.
this be reduced simultaneously with that of the sial by 0.1, then the figures of the table are only decreased about 5 per cent.
Thickness of block of sial in sima of specific gravity 3.0.
| Specific Gravity of sial. | 2.6 | 2.7 | 2.8 | 2.9 | 2.95 | ||
| Height of surface above sea-level |  |
100 m. | 24 | 32 | 48 | 96 | 192 km. |
 |
4000 m. | 53 | 71 | 106 | 213 | 430 km.„ | |
