Geography 



497 



rents wholly to change the climate of 

 western Europe. Such an arrange- 

 ment would be effected by the submer- 

 gence of the Isthmus of Panama and 

 adjacent country, allowing the equa- 

 torial current to pass into the Pacific. 

 The gale factory of the western Atlantic 

 would then be greatly reduced. 



The area south of the Cape of Good 

 Hope is another birthplace of great 

 cyclonic systems, the warm Agulhas 

 Current meeting colder water moving 

 up from the Polar regions ; but in the 

 Southern Ocean the conditions of the 

 distribution of land are different, and 

 these systems sweep round and round 

 the world, only catching and affecting 

 the south part of Tasmania, New Zea- 

 land, and Patagonia. 



MOVEMENTS OF THE LOWER STRATA 

 OF WATER 



In 1894 I spoke of the movements of 

 the lower strata of water in the sea as a 

 subject on which we were only begin- 

 ning to get a little light. Since that 

 year we have learnt a little more. It 

 is a common idea that at the bottom of 

 the sea all is still ; but this is a mistake, 

 even for the deepest parts, for the tidal 

 influence reaches to the bottom and 

 keeps every particle in motion, though 

 such motion is quiet and slow. 



Near the shore, however, though still 

 in deep water, the movement may be 

 considerably increased. Cases have oc- 

 curred in late years where submarine 

 cables have broken several hundred 

 fathoms deep, and when picked up for 

 repair it has been found that the iron 

 wire covering has been literally rubbed 

 away as by a file. This can only be the 

 result of an undercurrent along the bot- 

 tom moving the cable to and fro. Such a 

 current might be caused by a submarine 

 spring, for there is no doubt that much 

 fresh water finds its way into the ocean 

 in this fashion, but it is more probably 

 generally an effect of acceleration of the 

 tidal movement due to the rising slope 



of the continent. In connection with 

 this, further facts have come to light in 

 the course of recent marine surveys. 



Many isolated shoal spots in the great 

 oceans have figured in our charts, the 

 results of reports by passing sailors who 

 have said they have seen breakers in fine 

 weather. 



Such places are the terror of seamen, 

 and it is part of the duty of surveying 

 ships to verify or disprove them. Very 

 much has been done in the last eighteen 

 years, with the result that the majority 

 of them have, as dangers, disappeared. 

 In many cases, however, a bank has 

 been found, deep in the ordinary ac- 

 ceptation of the word, but much less 

 deep than the surrounding sea — solitary 

 ridges, in fact, rising from the ocean 

 floor. Frequently, in examining these 

 banks in search of shoaler spots, breakers 

 have been reported and recognized as 

 such on board the surveying ship from a 

 distance, but on approach they have 

 proved to be small overcurls caused by 

 tide ripplings, and the depth of water has 

 proved to be several hundred fathoms. 

 These ripplings are clearly caused by 

 the small tidal motion in the deep water, 

 generally in these cases of more than 

 2,000 fathoms, meeting the slope of the 

 submerged mountain range, being con- 

 centrated and accelerated until the water 

 finally flows up the top of the slope as a 

 definite current, and taking the line of 

 least resistance, that to the surface, 

 makes itself visible in the shape which 

 we are accustomed to associate with com- 

 paratively shallow water. 



These cases form remarkable instances 

 of the manner in which extensive motion 

 of water may arise from very small be- 

 ginnings. 



An observation I was anxious to make 

 in 1894 has been successfully carried out 

 since. This was to ascertain whether 

 there was any permanent undercurrent 

 in the Straits of Bab-el-Mandeb due to 

 more water being forced through the 

 straits on the surface by the persistent 



