348 SLM WMITS THOM SI QUO BIN IOS 
tion so as to give nearly uniform strikes. Unless closely observed 
it may not be noted that there are really minor rapid deviations 
of strike, which indicate a set of pitching folds, and a complexly 
folded district. The major and more important folds may be 
transverse to the minor plications. From what has gone before, 
it is plain that in such cases the important observations are not 
the strikes and dips of the strata of the minor folds, which vary 
momentarily, but the direction and pitch of the axes of the minor 
folds, which give the direction and amount of the dip of the major 
fold, and therefore the average strike. 
(5) Pumpelly has called attention to the fact that discord- 
ance between strike of bedding and that of secondary structures 
indicates pitching folds. Where a secondary structure develops 
at right angles to the greatest normal pressure, or nearly so, it 
in many instances has a nearly uniform direction for an extensive 
area. In case the folds are horizontal, or the district is simply 
folded, this direction is the same as the strike of the rocks or 
the strike of the axes of the folds. Where the forces producing 
the folds are in two or more directions, and consequently form 
complex folds, the minor component, producing pitch, does not 
develop cleavage at right angles to itself; and the relations 
between the strike of bedding and that of the secondary structure 
vary from near parallelism on the limbs of the longitudinal folds 
to a direction at right angles to each other at the ends of the 
canoes and on the crests of the anticlines and in the troughs of 
the synclines. In passing from one place to the other there are 
found all relations between parallelism and perpendicularity. 
Because the area where the two are parallel, or approximately so, 
is greater than the area where there is an important discordance 
between the two, it has been customary for text-books to speak 
of the strike of bedding and the strike of cleavage as usually par- 
allel. This, as has been seen, is wholly true only where the folds 
are horizontal, and the statement becomes more and more a par- 
tial truth as the pitch of the folds increases in amount —that is, 
as the less conspicuous folds become more important. Hence it 
is that where a secondary structure exists the relations which 
