Gale's 
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DEFORMATION OF ROCKS 347 
amount of the dip of the major folds. The average strike is, 
therefore, also determined. 
Of these three observations, the first is the only one ordinarily 
taken, and it is the one of the least importance in regions of 
close, complex folding. It is only by making the second and 
third observations that an adequate idea of the structure can be 
obtained. While the first observation may be made at any 
point, the second and third observations can be made accurately 
only along the crests of the anticlines or troughs of the synclines 
of the various orders of folds. Therefore, it may be necessary tc 
work over a considerable area in order to obtain the required data. 
Some practical suggestions may be offered as to the manner of 
determining whether or not the rocks of a district are complexly 
folded, and if so folded, the direction and pitch of the axes of 
each set of folds, and therefore the strikes and dips of the two 
sets of cross folds. 
(1) It is advisable to look for the ends of canoes. These 
may be frequently found at the ends of ridges; hence especial 
study should be made of the folds where a topographic break 
appears across the ordinary ridges, either at a right or an acute 
angle. When once theend of a canoe is found, an observation 
can be made as to the direction and pitch of the axes of the fold, 
and thus the strike and dip of the cross fold be determined. 
(2) The tops of ridges should be examined. These may be 
the crests of anticlines or the troughs of synclines, depending 
upon the topographic development of the region. Along the lit- 
tle cross breaks which are sure to occur, the direction and pitch 
of the axes of the folds may be determined. In some instances 
ridges are longitudinally inclined, following hard layers, and in 
this case there is an exceptionally fine opportunity to deter- 
mine the direction and pitch of the folds. 
(3) In case the two sets of cross folds are about equally con- 
spicuous, there may be a double set of ridges and valleys cut- 
ting each other at right angles, or nearly so, and this may givea 
clue to the character of the folding of the district. 
(4) In some cases the beds are closely plicated in one direc- 
