THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE III. VOL. III. 



No. III.— MARCH, 1886. 



ODRIO-TZDsT^-Ij ABTIGLES. 



I. — On the Permanence of Continents and Ocean-Basins, with 

 Special Reference to the Formation and Development of 

 the North American Continent. 



Ey Prof. Joseph Le Conte. 



UNDER the influence, perhaps, of the prevailing idea of evolution 

 in all things, the conviction has been growing in the minds of 

 geologists in recent times that the larger features of the earth's 

 surface have grown from the earliest times, and therefore that the 

 places of the continents and ocean-basins have been substantially 

 permanent. Prof. Dana is largely the originator and expounder of 

 this view, and he has applied it with great skill to the American 

 continent. But while I believe the view is substantially true, 

 I cannot but think that it may be, and has been, pushed too far. It 

 is true indeed that the opponents of the view have attributed to its 

 advocates a strictness in the use of the term ' permanent ' which they 

 have never urged. It is true that by permanence is meant only per- 

 manence of place, not of outline, and that substantial permanence is 

 not inconsistent with very large changes by oscillation, especially at 

 the end of the great Eras. But, making every allowance for such 

 latitude of meaning, there has been, undoubtedly, some confusion 

 of thought and looseness of statement on this subject. We give 

 a few examples. 



Prof. Dana in his admirable manual, p. 149, gives a figure (fig. 

 206), which he calls " Archaean map of N. America." This is really 

 a map of Areas of exposed Archcean rocks, and for such it is doubtless 

 intended. It cannot, of course, be a map of the land of Archcean 

 times (since Archaean rocks were formed on sea-bottom), but 

 is approximately a map of land of early Silurian times. But being 

 called an Archaean map of the continent, and being found in the 

 chapter on Archaean times, the inattentive reader is led to infer that 

 it represents land of that time ; more especially as the rest of the 

 present continent is spoken of and represented as submerged, and 

 therefore by implication this part as, then, land. And as Prof. 

 Dana afterwards treats these areas as the nucleus from which the 

 continent was developed, he seems to begin this development from 

 the land of Archcean times. I am quite sure that many have been 

 misled by this figure and the accompanying statements. 



Again, Prof. Chamberlin in his excellent " Geology of Wisconsin," 

 vol. i. p. 62, gives a map somewhat similar to Dana's, which he 



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