pala 
~ 
—— 
# 
avoir soulevé et rompu le sol pour 8 
Origin of the Continents of the Earth. 355 
stability of the superincumbent waters; I ask, can we safely make 
this affirmation, until we know doupetieiiag more certain than past 
investigations have revealed, about the geological history of the 
two-thirds of the surface of our planet that are concealed be- 
neath its oceans ? 
In our conclusion from. the above reasoning, we fall in nearly 
with the views presented by a distinguished French geologist, M. 
C. Prevost, who has argued with much force in favor of subsidence 
as acause of the apparent elevation of the land: though it may be 
night to state that these conclusions were arrived at previously to 
seeing his memoir.* There appear to be many objections to the 
opinions of M. Prevost, as they are expressed by him, inasmuch 
as no allowance is made or admitted for minor disturbances and 
actual elevations by subterranean forces. His views however are 
well worthy the attention of the geological enquirer. 
_ The principles explained place the general theory of change of 
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 ruptures, 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 Alleganies and like regions. 
sf The ples a theory of changes of lovel “A contraction and oxcanaias and the 
rise thus of continents, was first presented by Mr. Babbage and De la Beche. M. 
C. Prevost takes the different ground that all seeming elevations are the result of 
ence. His propositions are as follows, (Bulletin de la Soc. Geol. de France, 
ah cia’ & 1840, p. 186) :— a 
1. Que le relief de Ja surface du sob est le résultat de grands affaissements suc- 
sits, qui, par contre-coup, et d’une maniére secondaire, ‘ont pu oceasionner acci- 
dentellemen nt des élévations absolues, des pressio age des ploiements, des 
nts, mpeg des iaatagete des failles, etc. ; 
rte a er croire que ces ont été produits par une cause agissant sous 
sol, c’est-a-dire par une » force piers 
i sol sont des effets complexes de retrait, de contrac- 
tach ‘Que les dislocations du: 
Hon, de plissement et de chute ;” 
“3. Que les matiéres ignées (granites, pened trachytes, basaltes mie 
s’echapper, ont seulement pro te u- 
, lavas,) loin 
tions de continuité qui Jeur ont pe offertes par le retrait et les ruptures, pour sortir, 
Suinter et = een au-dehors 
Dis 
SO Aye Ry as * 
