ROCKS, THEIR KINDS, STRUCTURE, AND DISPOSITION. 
that which has been heaved up, an 
upheaval or hitch: where the strata 
at the slip lie at different angles, 
the slip is called a fault, as O. All 
such displacements of strata are 
known as dislocations, and they are 
much more frequent than the regu- 
lar disposition of rocks on the sur- 
face of the earth. When strata are 
bent in wavelike undulations, they 
are said to roll, as H; and the hol- 
low or concave portions are termed 
troughs or basins, and the elevated 
portions ridges, as I and K. 
2. Unstratified Rocks. — These 
rocks are thrown up amidst the 
stratified, and assume different 
positions according to the manner 
of their upheaval. Where they 
throw the strata into various angles, 
the rock upheaved is termed the dis- 
rupting mass, as V ; at other times, 
they overlie the other rocks, and 
are then called overlying, as E; 
they are also interjected between the 
other strata, and are said to be 
interstratified, as F. Sometimes 
they intersect the other strata by 
masses like walls, which are called 
dikes, asG ; and sometimes the dis- 
rupting mass breaks into branches, 
which are called veins, as N. 
When a broad face of rock is. 
exposed, and the different rocks 
shewn, as in a cliff on the sea-shore, 
a railway-cutting, or a quarry, such 
_ exhibitions of strata are called sec- 
tions ; and these may be delineated 
on paper. Sections of the under- 
lying rocks may also be made, by 
examining the different rocks in 
a country, though no section be 
exposed in nature. 


Fig. 80.—Section of the Different Kinds of Strata, 
to 
pS 
~~ 
rv 
= a 
a 
go 2 
8S gS & 
Dem — ~ 
Se S030 
Ga Sea. 
oa Hel BS Om 
ROT NOAR 
pred r!w 
Contorted or twisted strata, 
A seam. 
Rocks tilted up. 
Columnar basalt, 
Conglomerate, 
A fault. 
eee as NS) nee 
O 
P 
Q 
R 
Ss 
sf Y 
L, The dip of the rocks, 45°. 
M, An outcrop, 
H, Bent and rolling strata. 
N, Veins. 
G, A dike, 
I, A basin or trough. 
K, A ridge of rocks. 

able rocks. 
B, Inclined strata. 
A, Horizontal and unconform- 
C, A slip. 
D, A disrupting mass. 
E, Overlying trap, 
I’, Interstratified trap. 
