J. D. Dana on the Origin of Continents. 97 
the area, and an attending swelling of the surface, or else a rising 
of the strata into folds by lateral pressure.* 
The effects of lateral pressure might in many parts be local or of 
very limited extent. A contracting : area might be made up of sev- 
eral separate areas of Peres oe not acting together upon any 
particular line. Even supposing a whole quarter of our globe to 
exert laterally all the force possible, by a uniform contraction con- 
tinued till the surface was depressed eight miles in depth, the 
whole effect would be equivalent to a lateral dislocation of only 
twelve miles. And in this calculation, we make no allowance 
for upliftings over the contracting area, which would diminish 
the action; nor for a diminution of breadth in the surface of the 
area, which diminution must be going on if the surface is losing 
heat. In the remarks which follow relating to this point, Amer- 
ica, therefore, is not instanced as an example of what must every 
where have happened, but of what has here happened. 
The foregoing are the obvious effects of contraction. A Prince 
Rupert’s drop (a drop of unannealed glass) may be referred to for 
farther illustration. The exterior, owing to its Ries first, is 
under oe papas and each particle (or section ) in the surface, 
presses laterally upon its neighbor like a stone of an arch upon 
the one adjciniog, ; and hence the effect of a simple scratch in 
causing it to break to pieces, explosively. The earth, had it 
cooled uniformly over the whole exterior, (and were it made of 
a uniform homogeneous material,) would have been in the same 
circumstances, the whole crust being under immense tension, yet 
every where balanced, and therefore not apparent; but Popling 
unequally, the same actual amount of force has been exerted, yet 
at different periods, producing, in different parts and in different 
periods, fractures, de epressions and upliftings. 
We comprehend the effects described more clearly if we re- 
member, as we Pues the common statement, that the niga 
* With regard to the foldi = strata by lateral pressure, the theory was first 
nted by Sir James Sane Ory s. Ro mf Pee Edinb., vii, 85,) and the injection 
of granite, coupled with the. amin of pe land, ine suggested by him as a 
source of the pressure in the instances he m n vat A on re a 
on this subject, says, in his work on eivinane) published jn 1825, * ‘Phere is ! 
son to conclude that in most og a be; sniongi * ata, particu ularly ed pre 
were only aay indurated, have bee wrted ont bent ssf ie ce saa 
paar to give the appearance of heqieh aherations oF a 
what is in reality but the replication selaphowas ct 
In Beche applies the theory to the structure of a the Ae (Gee , (Geol. i Resarehen, » 
Aut Sir James Hall to pion ae i t besides the 
lateral se ukey general followed s a phy at to thi result. “But since the soft 
Strata are inelastic, and moreover, in t li "ik mgd re 
clude that there is sufficient vertical stared ieee ieee foreign Flas 
A small hand model a het dion in thi eas, a a chil 
model of a br to t 
Rocks se, Vol. ‘ir 1 No? Tote 13 
Jeeps 
