740 NATURAL SCIENCE. ^^^ 



evidence throughout of shallow water origin ; and that in this way 

 the continent was extended from the Archaean southward, south- 

 eastward, and south-westward. 



The evidence as far as the eastern half of the continent is 

 concerned was clearly manfest before 1845 (my first paper on the 

 origin of continents was published in 1846 in the American Jonrti. 

 Set., 2nd ser., vol. ii.), by which time the States of Connecticut, 

 Massachusetts and New York had been geologically surveyed, and 

 their final reports published, including a general coloured geological 

 chart of the country by James Hall ; and, besides, incomplete surveys 

 had also been made of some other States. Further, the Professors 

 W. B. and H. D. Rogers had so far completed the surveys of Penn- 

 sylvania and Virginia that they brought out in 1842 (Trans. Assoc. 

 Anier. Geol. and Naturalists) their admirable paper on the Appalachian 

 Mountain system, their flexures, &c. They showed that the flexing, 

 faulting and uplifting for the 1,000 miles of their length was a sequel to 

 the long series of Palaeozoic deposition, a folding of the strata from the 

 bottom (the Cambrian, as now called) to the top, confirming all other 

 evidence that the strata were continental formations, and the work, 

 regular continental growth. 



Afterwards the earlier Mesozoic (that is, the Jura-Trias), added 

 only brackish water or fresh-water beds, along some portions of the 

 Atlantic border ; and later the Cretaceous and Tertiary followed, 

 finishing the continent to its eastern limit. 



Similar facts complete the argument for continental permanence 

 as regards the western half. By permanence, as I have always said, 

 is meant, not the absence of deep subsidences, or of deep conti- 

 nental waters at times — say 2,000 or 3,000 feet in the interior, or on 

 the borders, but the non-occurrence of oceanic depths and alternations 

 with oceanic conditions. 



James D. Dana. 

 New Haven, Oct. 14, 1892. 



HI. 



I DO not wish to continue the discussion on this subject, but I 

 think that Dr. Wallace has not, in two instances at least, in his 

 letter published in the November number of Natural Scienxe, 

 quite understood my arguments. 



Dr. Wallace states that he cannot understand why tlie connection 

 between Africa and India by means of existing continental areas 

 would not suffice for the explanation of certain relations between 

 the faunas and floras of India and the Mascarene Islands, and why I 

 should prefer to bridge an ocean between 2,000 and 3,000 fathoms 

 deep, in order to reduce the distance slightly. I may say that I 

 do not regard the question of distance as material ; and the majority 



