426 J. D. Dana— Results of the Earth’s Contraction 
1. Have subsidences been produced by lateral pressure ? 
The theory of Professor James Hall, that the great subsi- 
dences of the globe have been made by the gravity of accumu- 
lating sediments, has been shown elsewhere* to be wholly at 
variance with physi cal law. 
Another theory is emia by Prof. LeConte, in his recent 
paper in the last volume of this Journal, to which the reader is 
referred. Admitting, with Prof. Hall, that the meam thickness 
of the accumulations in the Appalachian region of Pennsyl- 
vania is s 40, 000 ep and therefore that this is the measure - 
ave 7 ER in the aqueo-igneous fusion” and thus have 
added to the result. 
No _ cause of the gradual subsidence than that here cited 
is appe to. 
ow the whole of this contraction took place, if any occurred, #7 
the underlying Archean rocks (Azoic, or Laurentian and Huro 
: This Journal, Il, xlii, 210, 1866, III, v, 347, 1873; LeConte, ib., III, iv, 461, 
1872. 
+ The pal points in Prof. Hall’s theory of mountains, published in 1859, 
ed p- 341, eft this volume,) are 
. Coast regions 1 arena ce marine currents, and hence of deposited sedi- 
ments 
d 
. The of sediments ries Phere their = gradually sink the crust, an 
eng agreat et re is attained ; solidified and sometimes crys- 
tallized 
3. The aentincana afterward somehow raised—not the mountain regions sepa 
Tate! 
4. Shaping of the mountains out of other sediments ents by den 
5. Metamorphism due to “ motion,” “ fermentation,” and a iitde gen the heat 
coming up from below ar Abe inonnotiy consequence of the in- 
creasing 
In Prof. LeConte’s tt aia —— Sours. tt: iv, 345, 460, 1872): 
1. $A -aeptaiog los the sesh ae 
© ieee maciewon igneous softening of the ie Sata Nal ito dome 
smite aes a an dente together the region of ‘sedimentary accumulation, 
_ 4, The elevation of mountains due solely to crushing ed 
tne Sle bapng saan: me rise of the isogee 
