HOW TO OBSERVE, 
horizontal position, conformably upon each other, 
and a force should be exerted from beneath, in a 
direction perpendicular to their strata, sufficiently 
strong to eject the central mass T, is it not plain 
that, as they are elevated, the broken edges of the 
several strata will be piled up against the ejected 
mass ! To illustrate this still farther : Suppose, for 
example, we lay a double series of books on each 
other in a horizontal position, thus, and then elevate 
Fig. 16. 
Fig. 17. them by a force placed be- 
neath the line of junction, the 
edges, of course, would be 
raised up, and book would be 
piled against book, like the 
gable end of a roof, thus (fig- 
ure 17) : 
We sometimes find rocks elevated in this manner, 
without discovering any evidence of the cause that 
produced the change of position. The internal 
force may not have been sufficiently powerful to 
raise a mass of rocks to the surface, and yet suffi- 
cient to fissure the crust and tilt the rocks into a 
very elevated position, as in 
Fig. 18. 
