558 REPORT OF NATIONAL MUSEUM, 1904. 



In 1871, Dr. F. V. Hopkins, professor of geology, chemistry, and 

 mineralogy in the State University of Louisiana, issued a report on 

 the geology of the State, relating particularly to the post-Tertiary 

 deposits, and containing also a colored geological map. 

 Qeeiogy of Louisiana, These deposits he divided into (1) Drift, (2) Port 

 Hudson (so-called by Hilgard), (3) the Loess, and (4) 

 the Yellow Loam, the last three being included also under the general 

 name of Bluff Formation. 



Hopkins held (and Dana approved) that the Port Hudson and over- 

 lying beds were deposited when the land was at a lower level than 

 now, and that the loess was the accumulation over an old flood plain 

 of the Mississippi, as suggested by Lyell. The drift itself, however, 

 he conceived to be due to the agency of icebergs in a sea at least 1,159 

 feet deep in the Ohio Valley. To this last view Dana, of course, 

 objected. 



In 1872 the subject of the formation of the great features of the 



earth's surface, including, of course, the formation of mountains, was 



brought up once more by Joseph Le Conte, then professor of geology 



and natural history in the University of California. 



Le Conte's Ideas on . , . * " , 



Mountain Making, In a series of articles in the American Journal of Sci- 



1872. 



ence for this year he reviewed the ideas of Humboldt 

 and others; discussed the probable condition of the earth's interior, 

 whether fluidal or otherwise; and announced himself as convinced that 

 the whole theory of igneous agencies, which formed the foundation of 

 theoretic geology, should be reconstructed on the basis of a solid 

 earth. 



On the assumption that such an earth would be not homogeneous, 

 but that some areas would possess greater conductivity than others 

 and would, therefore, cool and contract more rapidly in a radial direc- 

 tion, he affirmed that the present sea bottoms represented the areas 

 of most, and the continents and mountain ranges those of less, rapid 

 cooling and contraction. This he felt was borne out by the researches 

 of physicists who had shown that the continental masses were less* 

 dense than suboceanic matter. 



To him the cooling earth might be regarded as composed of concen- 

 tric isothermal shells, each cooling by conduction. The exterior being 

 the first to cool and solidify, would, through the shrinking away of 

 the still cooling interior, become subjected to powerful horizontal 

 pressure or thrust, which as time went on would find relief in the 

 direction of least resistance (i. e., upward) and along lines of weakness. 

 It was, however, his idea that this yielding was not by upbending into 

 an arch, but by a mashing or crushing together horizontally like dough 

 or plastic clay, with more or less folding of the strata and an upswell- 

 ing or thickening of the whole squeezed mass. 



