742 NATURAL SCIENCE. ,„,,... 



existed where deep sea is now, or vice versa, that evidence must not 

 be summarily dismissed because it is opposed to a theory that, as it 

 appears to me, is \ery far from being satisfactorily established. 



W. T. Blanford. 



IV. 



Permit me to explain the passage in my article on this subject 

 which Dr. Wallace characterises as " an extraordinary claim." When 

 I wrote that " the present continents are the outcome of a long series 

 of mutations," each phase being " an episode in a long process of geo- 

 graphical evolution," I had in my mind a very different kind of 

 evolution from that assumed by Dana with respect to North America. 

 He regards the surface exposure of the Pre-cambrian rocks in Canada 

 as the nucleus of the continent, and believes North America to have 

 been built up by additions to this nucleus. In the case of America, 

 there does seem to have been a process of building up by additions 

 during Neozoic times ; but I maintain that neither America nor any 

 other continent dates back as a distinct continental plateau to 

 Palaeozoic times. 



The evolution I referred to was the gradual evolution of con- 

 tinents and oceans together out of a more generalised state of 

 geography. I look back to a time when the physical features of the 

 earth's surface were less accentuated than they are now ; when there 

 were neither oceans nor continents, but a more equal distribution of 

 land and sea all over the globe. 



I cannot see that Dr. Wallace's argument about the relative 

 displacement-capacity of continental masses and oceanic waters 

 proves the continents to have maintained the same -positions from the 

 earliest times. Dr. Wallace evidently fails to see the force of my 

 reply ; all his argument proves is that, // the volume of water has been 

 always the same, the total area of land at any period cannot have been 

 much larger than it is now, but in my article I showed that it was 

 unsafe to assume that the volume of ocean water is a constant 

 quantity. 



Again, what does Dr. Wallace mean by the great ocean-basins ? 

 and why does he object to the view that the Dolphin Ridge has once 

 been land ? To me it does not seem rational to speak of the Atlantic 

 as a single ocean-basin ; it is distinctly a double basin, and I can see 

 no reason why a large part of the Dolphin Bank should not have 

 been land, say in Triassic or Permian times. 



Dr. Wallace must remember that the geologist deals with a 

 length of time that reaches back far beyond the age of the modern 

 genera and families of terrestrial animals, and even if the distribution 

 of such animals can be explained by means of comparatively small 

 geographical changes, it is because most of these families do not date 



