CHAP. VI GEOGRAPHICAL AND GEOLOGICAL CHANGES 101 



General Stability of Continents loith Constant Cliange of 

 Form. — It will be observed that the very same evidence 

 which has been adduced to prove the general stability and 

 permanence of our continental areas also goes to prove 

 that they have been subjected to wonderful and repeated 

 changes in detail. Every square mile of their surface has 

 been again and again under water, sometimes a few hundred 

 feet deep, sometimes perhaps several thousands. Lakes 

 and inland seas have been formed, have been filled up with 

 sediment, and been subsequently raised into hills or even 

 mountains. Arms of the sea have existed crossing the 

 continents in various directions, and thus completely 

 isolating the divided portions for varying intervals. Seas 

 have been changed into deserts and deserts into seas. 

 Volcanoes have grown into mountains, have been degraded 

 and sunk beneath the ocean, have been covered with 

 sedimentary deposits, and again raised up into mountain 

 ranges ; while other mountains have been formed by the 



Tertiary volcanoes "which extended through Greenland, Iceland, the Faroe 

 Islands, the Hebrides, Ireland, Central France, the Iberian Peninsula, the 

 Azores, Madeira, Canaries, Cape de Yerde Islands, Ascension, St. Helena, 

 and Tristan d'Acunha, and which constituted as shown by the recent 

 soundings of H.M.S. Challenger a mountain-range, comparable in its 

 extent, elevation, and volcanic character with the Andes of South America" 

 {Geological Mag. 1874, p. 71). On examining the diagram of the Atlantic 

 Ocean in the Challenger Reports, No. 7, a considerable part of this ridge is 

 found to be more than 1,900 fathoms deep, while the portion called the 

 "Connecting Ridge " seems to be due in part to the deposits carried out by 

 the River Amazon. In the neighbourhood of the Azores, St. Paul's Rocks, 

 Ascension, and Tristan d'Acunha are considerable areas varying from 1,200 

 to 1,500 fathoms deep, while the rest of the ridge is usually 1,800 or 1,900 

 fathoms. The shallower water is no doubt due to volcanic upheaval and 

 the accumulation of volcanic ejections, and there may be many other 

 deeply submerged old volcanoes on the ridge ; but that it ever formed a 

 chain of mountains "comparable in elevation with the Andes," there 

 seems not a particle of evidence to prove. It is however probable that 

 this ridge indicates the former existence of some considerable Atlantic 

 islands, which may serve to explain the presence of a few identical genera, 

 and even species of plants and insects in Africa and South America, while 

 the main body of the fauna and flora of these two continents remains 

 radically distinct. 



In my Darwinism (pp. 344-5) I have given an additional argument 

 founded on the comparative height and area of land with the depth and 

 area of ocean, which seems to me to add considerably to the weight of the 

 evidence here submitted for the permanence of oceanic and continental 

 areas. 



