2S2 TIlcAniifiiilii (jioliKjixt . NoveinlxT, 1«ll 
piled upon it. it will coiitiiiiu' t<» sink, tlidii^li subject to vertieiil 
piilsjitioiis of level due to other causes, which it is not my object 
to treat of iiere. Hut there will eventually come a tinu' when the 
accumulated stresses of the e\[iandii)<r rocks will overcome the 
weiirht of sediment, and then the upheaval, foldinji. and Ijuildiuir 
of the mountain- chain will Ite^in. lint it is not t(; l)e su{)posed 
that the rise of temperatun' takes place with the mathematical 
precision descril)ed here for mere purposes of explanation*. I 
have shown that volcanic action often contributes to the foun(hi- 
tion materials of a mountain-ran*re. and that intrusive sheets and 
dykes penetrate the sediments, and ash beds are laid down before 
the initial movement usherin*; in the birth of the range takes 
place. It is evident from this that there will Ite i>;reat variations 
of temi)erature takinu' place in the foundation crust and tlie sedi- 
ments (hiriuii their layini: down. 
The whole series of rocks, volcanic and sedimentary, will form 
a comj)lcx which will be simultaneously. l)utditt'erentially. affected 
by till' foldiuii and elevation wlien that l»egins. 
I iilocknni tli( niiiiiHis. fiirrra iif tlit rartli. 
When once the elevation initiated only by i)ilin<>-up of sedi- 
ment, the sinking of the crust, and its conseiiuent heating — 
otherwise by the rise of the isogeotherms — is established, a move- 
ment of the interior heated matter of the earth must take place 
towards the axis or axes of tlu' range. 'I'liis is proved by the 
fre(iuencv of granitic cores in great mountain-ranges, by the vol- 
canic action accompanying their elevation, and its persistence or 
recurrence in a range even late on in its history, as instanced by 
*Tliis seems a fruitful source of difficulty with some minds, beginuiuir 
with Hopkins and ending with Huttou. Fisher, and ^liddlemiss. Tlieir 
position seems to be this: if the rise of the isogeotherms into the new 
deposits eventually wrinkles and lifts them, why does it not begin at 
once? Why, for instance, should not 100 feet in thickness cause a rise, 
and if it does, how can thick beds ever be deposited":' But there are 
thick t)eds, so the alleged priiinint mohili never acts. Q.E.I). 
After making, as 1 fondly thought, full explanation of the imxhix 
opn-iiiifh', I never anticipated ihe establishment of what a sense of 
humour compels me to call another yw/'.>< iixi/iormii. Even supposing the 
isogeotherms rose as rapidly as the deposits were laid down, the deposits 
could not be lifted until sufficient force accumulated to overcome the 
gravitation. But in a sinking area, as T have pointed out, if there be 
anything in the principle invoked, the presumption is that the isogeo- 
therms are in process of sinking also, and it may take a lengthened 
)>eriod of sedimentation before they begin as a series to move upwards. 
There are many other possible conditioning causes. A practical 
mechanical mind should soon see through tliis imaginarv difficulty. 
