Origin of Mountains. 431 
clinal of probably 4,000 feet, this much being registered by the 
thickness of the deposits ; but it stopped short of metamorphism, 
the sandstones being only reddened and partially solidified ; 
and short of plication or crushing, the strata being only tilted in 
a monoclinal manner 15° to 25°; it ended in numerous great 
longitudinal fractures, as a final catastrophe from the subsidence, 
out of which issued the trap (dolerite) that now makes Mt. 
Holyoke, Mt. Tom, and many other ridges along a range of 
100 miles.* 3 
These examples exhibit the characteristics of a large class of 
mountain masses or ranges. geosynclinal accompanied by 
sedimentary depositions, and ending in a catastrophe of plica- 
tions and solidification, are the essential steps, while metamor- 
phism and igneous ejections are incidental results. The pro- 
cess is one that produces final stability in the mass and its 
annexation generally to the more stable part of the continent, 
though not stable against future oscillations of level of wider 
range, nor against denudation. 
It is apparent that in such a process of formation elevation 
by direct uplift of the underlying crust has no necessary place. 
he attending plications may make elevations on a vast scale 
and so also may the shoves upward along the lines of fracture, 
and crushing may sometimes add to the effect; but elevation 
from an upward movement of the downward bent crust is only 
an incidental concomitant, if it occur at all. . 
_ We perceive thus where the truth lies in Professor LeConte’s 
important principle. It should have in view alone monogenetic 
mountains and these only at the time of their making. It will 
then read, plication and ava along fractures being made 
more prominent than crushing: 
Plication, shoving along fractures and crushing are the true 
Sources of the elevation that takes place during the making of 
geosynclinal monogenetic mountains. 
And the statement of Professor Hall may be made right if 
we recognize the same distinction, and, also, reverse the order 
and causal relation of the two events, accumulation and sub- 
sidence; and so make it read : 
Regions of monogenetic mountains were, previous, and prepara- 
tory, to the making of the mountains, areas each of a slowly pro- 
gressing geosynclinal, and, consequently, of thick accumulations of 
sediments, 
The prominence and importance in orography of the moun- 
tain individualities described above as originating through a 
* This hi is precisel ich I have given in my Manual of Geology, 
though ‘witoat recogising the parallsn In at with the history of the 
