2S4 III' Alii'iurilii a, (iliHJisf . Nc.v.Mnh.T, IMIl 
It has lu'cii OS crlookcW that I liavf ali'caily t'X|)hiiii('(l that the 
wt'iijht of the mass alone will. Iiy coiiiiJi'i'ssivc cxtciisioii. consoli- 
date the Iti'ds hclow l»y ivdiiciuji" t lit'ir t hickncss. Also the (h-nsiT 
st'dimcntaiT rocks are often densei- only by infiltration. Tiiis is 
particiilaih t he case with sandstones, where the convei'sion into 
the tinal .-^taue of (|nartzite is liy the deposit of secondary silica 
in the intefspaces of the grains, not l)y condensation. 
('lavs contract on heatinu:: l»nt. accordinii' to my \iews. the 
contraction of snch beds in an eai'th-tronu'h will l>e vertical only, 
liv reason of the superimposed weight. .\ sta<i(' of metanior- 
phism is at least arrived at, as we see in clay-slate, when the ma- 
terials of that rock, ()ri<iinally clay, lieconie metamorpliost'd so us 
to behave like other rocks, and expand with a rise of ttMuperntnre. 
Kvi'n if thes«' ci'iticisms possess much force, they do not apply 
to the rocky crust of the eaith already consoli<lated fornrum' the 
earth-trough in which the sediments are laid down. There will 
be little or no loss by condensation in them, only straining or 
change of form. It is ol»vious that deep-seutt-d rocks must be 
so compressed by simple gra\itation, that lateral pressure will 
have little etfect in further condeusiag them. 
Ri ill nciit I x pii i\xii)ii ciniinhifirc in its iffrcfx. 
If a gi\en area of the crust of the earth is raised in tempera- 
tui'c. when the limit of elasticity is reaclu'(l the sui-plus material 
must be disijosed of l>y a change of form, it will rise in the line 
of least resistance. 
Assume that the surplus due to the culiical exjKiiision of a 
horizontal sheet is thrown into a ridge, and that then a fall of 
tempeniture takes placi' to the same extent. The material ridged 
up can nevt'r bcTdrawn l)ack again; it Itecomes a permanent feat- 
ure of the earth's surface. The contraction must lie satislied in 
another way. citlici- liy breaking up into lilocks. faulting and suli- 
sidenci' extending through its sul)stance. or liy Nt'i'tical contrac- 
tion aloiu'. and the lengthening of the lieds liy compressive exten- 
sion due to the weight of superimposed materials. Probably 
both these [irinciples generally come into operation together in 
nature. The earth is bound to I'etain its s<ilidity in whatever way 
that may lie satislied. If a rise of tenipeiature t hen succeeils. 
the effect will lie as liefore. and defoi-matitui will result, its locality 
l>ein<i"delermine(l liy the line of least resistance. 
In the case of a mountain-rang*' it will take place along or 
