MINERALS AND GEOLOGY OF CANADA. 449° 
is shewn also by the frequent presence of rows of pebbles, fossil 
shells, &c., parallel with the planes of stratification, as in fig. 56; by 
the occasional presence of the fossilized stems of trees (evidently in. 
their positions of growth) standing at right angles to these planes: 
(fig. 57) ; and sometimes by the presence of stalactites suspended in 
a similar position. 
The inclination of strata is technically termed the dip; and the 
direction of the up-turned edges, the strike. The dip and strike are 
always at right angles. In observing the dip, we have to notice both 
its angle or amount, and its direction,—as north, north-east, N10°E, 
and so forth. The direction of the dip is of course ascertained by 
the compass; the rate of inclination, by the eye, or by an instrument 
called a clinometer. The most convenient instrument for both pur- 
poses, is a pocket compass, furnished, in addition to the needle and 
graduated limb, with a moveable index hanging from the centre of the 
compass and playing round a graduated arc, as in the annexed out- 
line (fig. 58.) When the line A—B 
is held horizontally, the index J hang- 
ing perpendicularly, cuts the zero 
mark of the graduated arc. From 
each side of this point, the gradua- 
tion is carried up to 90°. If, con- 
sequently, the line 4—B be placed 
parallel with the dipping beds of any 
strata, the angle of the dip will be 
at once shewn by the index. A con- 
trivance of this kind, exclusive of the compass, may be easily made 
out of a semicircle of hard wood. The index may consist of a piece 
of twine extending below the graduated limb, and kept taut by a lead 
plumb or by a stone. 
When strata dip in two directions, the line along the culminating 
point of the strata is termed an anticlinal or anticlinal axis (= a in 
fig. 59); and the line from which the strata rise (= s in fig. 59), is 
called a synclinal or synclinal avis. Synclinals when of a certain 
magnitude, constitute ‘valleys of undulation.” Anticlinals are also 
often hollowed out by denudation, forming valleys or troughs called 
“valleys of elevation” (= e¢ in fig. 59.) The term “elevation”’ ap- 
plies here, however, to the raised strata, and not to the actual position 
of the valley, as many of these so-called valleys of elevation lie in the 
