'2Si) Tin Ann I'icii II (r('()Jn</ixf. T^ovenilter, ISfll 
Ynliii ii'k' ticft'iiii oft I II ciiiiti iiijinriiiiiiiiis iritli llii I il 1/ 1 ii<i-il<>ir ii iif 
iiKitiriiils fur Mnuiitiii n-hiilhl iii<i. 
('ouU'iuporanc'ous intrusive sheets of volcanic rock are a com- 
mon occurrence in st»me part of tlic sedimentarv history of a 
mountain-ran>re. In addition, it is freriuently found that vol- 
canic asiics hiid down in water, or subaerially. have a hirge de- 
velopment in rocks comi>osing mountain-ranges; and necessarily, 
if these occur, dykes and volcanic rocks of the same age must 
exist in the foundation materials of the range. 
DvXAMirAI, PKINCIIM.KS. 
Every theory which has hitherto l>een proposed to account for 
the elevation of mountains and the folding of the .stratified beds 
forming the earth's crust hinges finally on changes of tempera- 
ture. Thus the tangential force generated in a rigid crust of low 
temperature by the cooling and shrinking of the eaith's nucleus 
has been invoked to account for the crumpling of the crust into 
mountain-ranges: the crumpled skin of a dried apple being the 
stock illustration. In this case, the force called in is continuous 
contraction by loss of heat. The theory which T have elaborated 
is one dependent upon oltcrnntlons of temperature in the crust, 
contraction and expansion both being agents of uplift and lateral 
pressure. 
Jiiisiiis of J)< pnsitioii iind Tjomliiiij of flu lurtli s crust. 
It has already Iteen shown that the estaVtlishment of basins of 
deposition is the condition precedent to the building of a moun- 
tain-range. There can be no dejjosition if there is not land-area 
enough either in the shape of continents, islands, or active vol- 
canic oritices. or all combined ov successive, to yield the neces- 
sary sediment. This furtherniori' inij)lies considerable stability 
of conditions over lengthened periods of time combined with local 
mutations and changes of level, and. as I have indicated, we have 
the hi.storv of these nnitations within the rocks of a range. The 
distribution of sediments is dependent upon the depth of the 
water surrounding the land and the currents of the sea (when 
they are not laid down in lakes or subaerially by rivers) : Itut. 
whatever the conformation of the coast and sea-bottom, a con- 
tinuous discharge of sediment upon it must in time load it. and. 
as proved liy the enormous thickness of rocks composing great 
