76 ON SOME POINTS IN DYNAMICAL GEOLOGY. [VII. 



New York, November 12, 1872, I adduced a further argument 

 in favor of such a pre-palaeozoic continent to the eastward, 

 from the climatic conditions of great dryness which gave rise 

 in the palaeozoic region of North America to deposits of salt, 

 gypsum, and dolomite over considerable areas from N"vo, 

 Scotia to Michigan and Ohio, and from the time of the Cal- 

 ciferous formation to the Lower Carboniferous. (Engineering 

 and Mining Journal, January 14 and 23, 1873.) 



In concluding his essay, Professor LeConte declares that an 

 important problem in geological dynamics remains, in his opin- 

 ion, unsolved, namely, the cause of those "great and wide-spread 

 oscillations which have marked the great divisions of time, and 

 have left their impress in the general unconformability of the 

 strata " ; the last being that of the post-pliocene period. Now, 

 it is precisely the upward movements of this kind which con- 

 stitute the continental elevations of De Montlosier, Hall, and 

 myself, giving rise to plateaus, and by the partial erosion and 

 denudation of these to mountains. The cause of these conti- 

 nental elevations was not discussed by Hall, and is by LeConte 

 declared to be unexplained ; while such is the case, " the ac- 

 tual mountain-formation," to use his words, is still unaccounted 

 for. That these gentle and widespread movements of oscilla- 

 tion are, however, in some way not yet clearly explained, con- 

 nected with the contracting of the nucleus and the consequent 

 conforming thereto of the envelope, we can scarcely doubt ; or 

 that the latter, from its nature and origin, must present great 

 differences in constitution and in flexibility in its various parts. 

 From this it might be expected that the movements imparted 

 to the envelope alike by the process of secular cooling and con- 

 traction of the nucleus, and by the disturbance of the <'<|\iilil)- 

 rium of pressure consequent on the processes of erosion ami 

 sedimentation, would give rise to seemingly irregular oscilla- 

 tions, resulting in the depression or the elevation of con 

 able areas, constituting continental movements. 



The grave question here arises as to whether the heat which 

 plays such an important part in the phenomena under con- 

 sideration is a cause or an effect of the activities beneath the 



