OrKJin nf Jf(niiifii/ii RdiKjix. — Riddi'. 2S3 
the Andes, liookies. and the mountains of tlie Caucasus, where 
A'olcanie cones surmount some of tlie highest granitic peaks, show- 
ing that these are the lines of least resistance through which the 
interier forces of the earth expend themselves. 
Hi'iitimi of till' r<iil,-s iif tin: Moiiiitiiiii-llii ii<i< rccn rrciii <in<l coii- 
strtiit/i/ rciicircil (/ifrijKf ifs hisfari/. 
It is thus seen that tlie heated interior matter of the earth is 
constantly being drawn towards and injected into the constituent 
framew<n'k of a mountain-range. When once the elevation of 
the sediments consolidated into rocky matter in the earth-trough 
begins thnMigh the intluence of lateral pressure and the expand- 
ing mass 1>eiieath. a reduction of i)ressure and increase of volume 
takes place in the underlying fused rock. The compressive 
-Stresses of the rigid rock are partially relieved by folding and 
upward How, and the temperature of the mass falls. Additional 
fused matter has been drawn from the interior, and in i)rocess of 
time the rocks of the range begin again to rise in temperature. 
iSuch fluctuations of temperature are well shown in the intermit- 
tent character of volcanic action. After a great outflow of lava, 
a A'olcano is (quiescent, sometimes for centuries. It has lost so 
much matter and so much heat, but the forces accumulate 
<luring the time (»f ([uiescence to burst forth with renewed vigor. 
♦Such intermittent activity 1 conceive is what takes place on a 
larger scale in the history of a mountain-range, but with greater 
time-intervals. 
Df/ii((ia!cal Kjfccf nil titr sfriifd of till criinf In/ llisi of 
T(:in.j)cri(tii ri . 
The effect of a rise of temperature on the rocks of tlu' earth is. 
excepting in the case of unconsolidated clays, to increase their 
bulk. Frcjm a gicat numVuM- of experiments made by me on 
sandstone, slate, limestone, and marhlc. \ have estimated the co- 
efficient of exijansion of average rock at 2.75 feet lineal per mile 
for every rise of 1(KI° Fahr. : but there is every reason to believe 
that the coefficient of ex|)ansion rises at higher temperatures than 
th<)S(! at which my experiments were conducted. It has Ix'cn 
urged by some of my ciitics that T have not allowed for the com- 
pression of the seiliments lilling the earth-trough into denser 
masses, but have credited all the expansion to mountain-building*. 
*Hutton, Presidental Address, Section C, ^Melbourne Meetini; of the 
Australasian Association for tlie A<l\anccnient of Science, j). s<». 
