MOUNTAINS AND THEIR ORIGIN. Ill 
ture on some of these extravagances in moun- 
tain-formations, a friend said to me, not inaptly, 
— “ One can hardly help thinking of these ex- 
traordinary contortions as a succession of frantic 
frolics : the mountains seem like a troop of rol- 
licking boys, hunting one another in and out and 
up and down in a gigantic game of hide-and- 
seek.” 
The width of the arch of a mountain depends 
in a great degree on the thickness and flexibility 
of the beds of which it is composed. There is 
not only a great difference in the consistency of 
stratified material, but every variety in the thick- 
ness of the layers, from an inch, and even less, 
to those measuring from ten or twenty to one 
hundred feet and more in depth, without marked 
separation of the successive beds. This is ac- 
counted for by the frequent alternations of sub- 
sidence and upheaval ; the continents having 
tilted sometimes in one direction, sometimes in 
another, so that in certain localities there has 
been much water and large deposits, while else- 
where the water was shallow and the deposits 
consequently less. Thin and flexible strata have 
been readily lifted into a sharp, abrupt arch with 
narrow base, while the thick and rigid beds have 
been forced up more slowly in a wider arch with 
broader base. 
Table-lands are only long unbroken folds of 
