610 THE JOURNAL OF GEOLOGY. 
level by contraction upon something better than a hypothetical basis, 
and are believed to explain the actual causes by which the changes have 
been produced. They correspond moreover with the view that rup- 
tures, elevations, foldings and contortions of strata have been produced 
in the course of contraction. The greater subsidence of the oceanic 
parts would necessarily occasion that lateral pressure required for the 
rise and various foldings of the Alleghenies and like regions.”’* 
The theory was further elaborated in the following year in three 
papers which appeared in the American Journal of Science ‘On 
the origin of Continents ;’’*? ‘Geological results of the Earth’s 
Contraction in consequence of cooling,”3 and ‘Origin of the 
Grand Outline features of the Earth,’* and was finally put into 
systematic form in his Manual of Geology. 
The general contraction theory was not original with Dana, as 
he acknowledged in these papers. He found it advocated by 
Leibnitz in 1691. Babbage and De le Beche had formulated the 
general theory of changes of level by contraction and expansion 
and the rise of continents. Mather, Elie de Beaumont, Lyell 
and others had made more or less reference to the principle, and 
M. Constant Provost had published in 1860 his view that the 
agency of contraction alone will account for the various changes 
of level which the continental areas have undergone. There were 
however certain features which were his own, as shown in the 
following passage: 
“The reader will perceive that although the main principles of 
Provost are sustained by the writer in this and his former paper, the 
manner in which these principles are carried out, is in some respects 
a little different, especially in the idea that the oceanic areas have been 
the more igneous parts of the globe, and for this reason have contracted 
most; that certain orographic changes over the continents are due to 
contraction beneath the oceanic regions, and that the fissurings and 
mountain elevations have for this reason taken place in some instances 
near the margin of a coutinent, or near the limit between the great 
“Am. Jour. Sci. Il, Vol. IL., p. 355. 
?Am. Jour. Sci. II., Vol. III., p. 94. 
3 Loc. cit., p. 176. 
4 Loe. cit., p. 381. 
