222 THE VOYAGE OF H.M.S. CHALLENGER. 



We may for the present, for the purpose of showing the extent of the bathymetrical 

 range, subdivide the preceding table into three groups, which I will call the Littoral, the 

 Continental, and the Oceanic or Abyssal. 



The divisions into littoral, continental and abyssal or oceanic are not arbitrary ; they 

 represent in the present state of our knowledge of the depths of the oceans, bathymetrical 

 lines of great physical importance. The littoral fauna extends over that shallow area 

 of the shores which is merely the extension under water of the shores themselves (to 100 

 or 150 fathoms) ; the continental line represents the extent to which we may fairly 

 assume that the lines of continents have been modified, the limits within which probably 

 subsidence and elevation as affecting continental masses, or rather their shores, have 

 taken place, to 450 or 500 fathoms, while the third region beyond this, that which has 

 been called abyssal or oceanic, undoubtedly represents those large areas of the ocean floor 

 which have remained unaffected through long geological periods. This view is gradually 

 gaining ground among geologists, and was one of the very first results arrived at by the 

 late Professor Agassiz in his discussions of the results of the dredgings of Mr Pourtales in 

 1866 and 1867. He had previously followed Guyot^ and Dana^ and come to the con- 

 clusions that the present continental areas, or at least their skeletons, are of very ancient 

 origin, and that the great oceanic basin had remained practically undisturbed from the 

 earliest geological periods.'' It may not be out of place to repeat here a part of Professor 

 Agassiz's argument : — " From what I have seen of the deep-sea bottom I am already led 

 to infer that among the rocks forming the bulk of the stratified crust of our globe, from 

 the oldest to the youngest formation, there are probably none which have been formed in 

 very deep waters. If this be so, we shall have to admit that the areas now respectively 

 occupied by our continents as circumscribed by the two hundred fathom curve or there- 

 about, and the oceans at greater depth, have from the beginning retained their relative 

 outline and position ; the continents having at all times been areas of gradual upheaval 

 with comparatively slight oscillations of rise and subsidence, and the oceans at all times 

 areas of gradual depression with equally slight oscillations." The same view has been 

 adopted by Geikie.* 



This was practically the same view developed by Thomson in the Depths of the Sea, 

 and previously in a lecture delivered before the Royal Institution in April 1869, and the 

 subject was greatly advanced by the analysis made by Mr Murray' of the nature of the 

 deposits on the ocean bottoms as contrasted to those which constitute the crust of the 

 globe. Dr Carpenter " has also further developed this view of the great antiquity of the 

 oceanic basins. 



1 Earth and Man, 1856. 



2 J. D. Dana, Manual of Geology, 1863, p. 732 ; Proc. Am. Ass. Adv. Science for 1873 ; Am. Journ. of Science, 1873. 



3 L. Agassiz, Nov. 1869, Bull. Mus. Comp. Zool., vol. i.. No. 13. * Geograpliical Evolution, 1879. 

 ^ John Murray, 1876, On Oceanic Deposits, Proc. Roy. Soc, No. 170. 



8 W. B. Carpenter, 1880, Lecture before the Royal Institution, January 23, 1880. 



