I. 



Further Observations on the Permanence of 

 Oceans and Continents. 



I. 



^PHE literature relating to the much-debated permanence of ocean 

 1 basins increases fast, and two fresh contributions have lately 

 ^been made to it. In the American Journal of Science for September 

 .(vol. xliv., p. 183), Mr. McGee writes on "The Gulf of Mexico as a 

 Measure of Isostasy"; while in iheQnarterly Journal of the Geological Society 

 for November (vol. xlviii., p. 519) Mr. R. J. Lechmere Guppy treats of 

 " The Tertiary Microzoic Formations of Trinidad, West Indies." 

 The authors, however, approach the subject from totally different 

 points of view, and it may be of interest to compare their results. The 

 subject is an interesting one, but the unbiased geologist will be much 

 perplexed with the conflicting opinions expressed by the various 

 authorities. 



Mr. McGee starts on the assumption that the earth's surface is 

 in a state of nearly stable equilibrium — hydrostatic equilibrium he 

 calls it, but we do not like the term to be applied to so imperfect 

 a fluid as the earth's crust. This equilibrium is indicated by the 

 fact that the crust is densest under the sea and lightest under 

 mountain ranges; therefore, as long as there is no transfer of matter 

 from place to place the dense sea-bottom will balance the lighter 

 mountains. Rivers, however, gradually transfer the land to the 

 bottom of the sea ; consequently the loaded sea-bottom will con- 

 tinually subside, perhaps carrying with it the adjacent flat shore, 

 while the unloaded continental areas will slowly rise. 



As an abstract proposition no fault can be found with this argu- 

 ment ; but no quantitative measurements of the earth's density sufficient 

 to prove any near approach to a hydrostatic equilibrium have yet 

 been made. When, also, Mr. McGee points to estuary after 

 estuary as showing recent subsidence, we cannot help observing that 

 he does not always clearly distinguish between loss of land from 

 marine erosion and true subsidence. He also makes no allowance 

 for the slow compression that estuarine deposits are always under- 

 going, as the organic matter decays and the particles pack closer. 

 The historical evidence for the post-Roman subsidence in Holland is 



