xxxviii GENERAL SUMMARY OF SCIENTIFIC AND 



than a liquid nucleus to the globe; and Leconte has just re- 

 hearsed the many arguments in favor of this view, adopting 

 the conclusions long since formulated on this subject by- 

 Hunt, who for the past fourteen years has maintained this 

 theory, and endeavored, in accordance with it, to explain all 

 volcanic and plutonic phenomena, on the supposition that 

 they have their seat in the lower regions of the stratified and 

 water-impregnated deposits of stratified rocks, and not in un- 

 stratified regions below. The great question of the origin 

 of mountains, which has been discussed recently by Dana and 

 by Whitney, is resumed by Leconte, who puts forth a new 

 explanation, according to which the elevation is due to later- 

 al pressure producing a vertical extension of the compressed 

 sediments. Hunt, however, has shown that such a process of 

 lateral compression is but an accident in mountain elevation, 

 and insists upon the view which regards mountains as but 

 the results of erosion of strata raised by continental move- 

 ments, as originally maintained by Montlosier, by Lesley, 

 and by Hall, the latter of whom long since ably expound- 

 ed the view, and illustrated it by reference to our American 

 rocks. The cause of continental oscillations is still obscure ; 

 but it is clear that it is to upward movements of this. kind, 

 and to the partial erosion of the areas thus uplifted, that 

 mountains are due, and that the nearly horizontally stratified 

 Catskills of New York have not had a different origin from 

 the far older and almost vertically bedded Highlands of the 

 Hudson. 



The continued researches throughout the year of Professor 

 Hayden in the Yellowstone region, of Lieutenant Wheeler in 

 Arizona and Nevada, of Professor Powell in the Colorado, 

 of Mr. Clarence King and his party in various parts of the 

 West, and of numerous other specialists, including also the 

 various state geological surveys, have greatly added to the 

 information at our command, resulting not only in an im- 

 proved knowledge of the stratification, structure, and geo- 

 graphical distribution of the rocks in general, but also of the 

 animal and vegetable remains included in their beds. An im- 

 portant discovery by Professor Powell is that of the occur- 

 rence of a system of gigantic faults in the Colorado region, 

 where the slip of the strata in places amounts to 2000 feet. 



Most remarkable discoveries have been made by Professor 



