ON THE NATURE OF IGNEOUS INTRUSIONS 189 
which has been eroded away from a large area, is 18,500 feet, 
and in the axial region of the mountains, is 25,000 feet. 
From the broad oval summit of the great dome we have 
restored in fancy by prolonging the remnants of the base of the 
arch over the central granitic peaks, we can see lesser domes 
which form a series and lead step by step down to the Little Sun 
Dance dome, a mile in diameter, the inner layers of which 
remain to this day unbroken. 
As the type of mountain briefly described above is distinct 
from other types usually recognized, it will be convenient to 
designate it by an appropriate name. To meet this want, I ven- 
ture to suggest that uplifts which owe their origin to the intrusion 
of a molten magma into the rocks beneath them, be termed 
subtuberant mountains. They may be fancied to originate from 
the growth of a tuber within the earth’s crust. 
General conclusions —From the facts to which attention has 
been directed, it seems to me that a sequence is traceable 
between: (1) Intruded sheets of the Palisade type, formed by 
highly fluid magmas spreading widely between horizontally strati- 
fied beds, and lifting a broad cover without producing conspicuous 
topographic changes or marked disturbances in the upraised beds. 
(2) More local intrusions of less fluid magmas forced into hori- 
zontally stratified beds, which raised the strata above into domes, 
as is the case of the Henry Mountains, the Sun Dance hills, etc., 
and (3) deeply seated intrusions probably of highly viscous mag- 
mas, which raised vast domes of sedimentary rock and the floor of 
metamorphic rock on which they repose, as in the case of the 
Black Hills, Big Horn, and Park Mountains. 
To the question, whence came the force that was enabled to 
intrude sheets of molten material scores and even hundreds of 
square miles in area, between sedimentary layers, and lift beds 
of rock of the same extent and, in at least some instances, many 
hundreds of feet thick; or elevate domes from 50 to 200 miles 
or more in diameter, to a height of several thousand feet, only 
general answers can be given. 
On the theory that the interior of the earth is in a highly 
