in the Twenty Years before 1895 55 



rock. The landing of the cables on the islands of Teneriffe, 

 Gran Canada, and especially La Palma, was no easy matter, 

 and an enormous number of soundings were taken, during which 

 it was conclusively shown that the valleys which form so 

 remarkable a feature of the islands are continued with much 

 the same features under the sea, and down to a depth of 700 

 or 800 fathoms. This was an important observation as a fact 

 in the morphology of islands ; it was also commercially valuable, 

 as the cables were, in the end, laid in a bed, where they remained 

 in good order for many years. The very detailed sounding 

 work made in this expedition showed how great the advantage 

 of it may be; and when surveying the route for the West 

 African cable, to connect up places along the coast, from 

 Conakry, near Sierra Leone, on the north, to St Paul de Loando, 

 on the south, it was surveyed in a series of profiles, run from 

 the deep water to within the loo-fathom line, or in the reverse 

 lin-ction. The rule in running these profiles was to have 

 soundings not differing by more than 200 fathoms. The 

 steepness of the continental escarpment varies considerably 

 round the Gulf of Guinea, in certain positions being quite 

 precipitous, in others very gradual. The average slope of 

 the steep part of the escarpment was about 150 fathoms in 

 the nautical mile; that is, the tangent of the inclination 

 was 0-15, and the angle 8. Near Cape Three Points the 

 slope was as much as 322 fathoms per nautical mile ; whence 

 the tangent of the inclination is 0-322, and the angles 18. 

 I h- approaches to the volcanic islands, St Thomas and Principe, 

 had to be surveyed, and, as in the Canaries, they were found 

 very steep, and with submarine valleys. Here a slope of as 

 much as 356 fathoms in half a nautical mile was measured, 

 giving the tangent of the slope 0712. and the angle 35!. h 

 precipitous slopes on land be examined with reference to tin- 

 ratio of height to horizontal distance, which gives the tangent 

 of the slope, these slopes will be found to be steeper th.m tin 

 average of precipitous mountainsides. On the moderately 

 steep parts the soundings were taken at distances of i nan 

 mil.- apart; where the slope was gradual, at 2 miles apart. 

 In work of this kind, the great < nee of the unit- 



