6o PROCEEDINGS OF THE GEOLOGICAL SOCIEXr. 



It will perhaps tend to render my treatment of the subject 

 clearer, if I point out at the outset that there are three possible ex- 

 planations of the phenomena presented to us by the present and 

 past conditions of the land and by the distribution of terrestrial 

 life ; these are : — 



1. That the present continental areas, including the shallow seas 

 around them, and the present oceanic tracts with a depth exceeding 

 about 1000 fathoms, have been the same since the original consoli- 

 dation of the earth's crust. 



2. That the continental and oceanic areas are not permanent, but 

 that they are from time to time interchangeable. 



3. That the continental and oceanic areas are permanent as a rule, 

 but that portions of them have at times passed from one condition 

 to the other. 



I propose to take in order the principal physical, geological, and 

 biological arguments in favour of the permanence of ocean-basins, 

 and to inquire how far they are conclusive, and especially whether 

 any exceptions are probable. I wish also to call your attention to 

 a few facts, mainly referring to the distribution of terrestrial or- 

 ganisms, that I think worthy of the attention of geologists. 



The permanence of the land- and sea-areas is no new idea. It 

 would be easy to quote from ancient and modern poets and writers 

 a series of extracts to show the prevalent belief in the fixed limits 

 of the ocean-tracts. It is only of late years, since the teaching of 

 Lyell and other modern geologists has become generally received, 

 that the old belief has been replaced by free speculation on the dis- 

 tribution of land and water in past periods. Under these circum- 

 stances, scientific men who revert to the ancient faith suffer from 

 the serious disadvantage of leading an enthusiastic school of fol- 

 lowers, who have never renounced the creed of their ancestors, and 

 who hail the convert to orthodoxy with the traditional joy over a 

 repentant sinner. There is always a risk of a sound scientific 

 theory being accepted in a much wider sense than was intended by 

 its original advocates, and the risk is extreme when the theory 

 coincides with the popular taste. 



The chief arguments brought forward in favour of the permanence 

 of ocean-basins or deep-sea areas are the following : — 



I. The higher specific gravity of the earth's crust beneath the 

 ocean, as inferred from pendulum observations, and the further in- 

 ference that these areas of greater density have been the same siuce 

 the original consolidation of the earth. 



