~ 
Pant IV] ANTICLINES, SYNCLINES. 517 
dome-shaped elevation of the strata, wherein, as if pushed up from a 
single point, they slope away on all sides from the | 
eentre of greatest upthrust, with a qud-gud-versal dip. 
Where the top of the dome has been removed the 
successive outcrops of the strata form concentric rings, 
the lowest at the centre, the highest at the circum- 
ference (A in Figs. 231 and 252). — 
Anticlines and Synclines.—But in the vast 
majority of cases the folding has taken place, not 
round a point but along an axis. Where strata dip 
away from an axis so as to form an arch or saddle, the 
structure is termed an Anticline, or anticlinal 
axis (Fig. 257). Where they dip towards an axis, 

REMOVAL OF BEDS, AS SHOWN BY THE DOTTED LINE @ ¢ ABOVE 
THE Axis b. 
forming a trough or basin, it is called a Syncline, 
or synclinal axis (Fig. 238). An anticlinal or 
synclinal axis, must always die out unless abruptly 
terminated by dislocation. In the case of the anti- 
cline the axis, after continuing horizontal, or but slightly 
inclined, at last begins to turn downward, the angle of 
inclination lessens, and the arch then ends or ‘noses 


Fic. 238.—TRovuecH, OR SYNCLINE, WITH STRATA (ac) RISING FROM 
Each SmpzE oF A CenTrRAL Axis 0, 

out.” Ina syncline the axis eventually bends upward, 
and the beds, with gradually lessening angles, swing 
round it. In a symmetrical anticline or syncline the 
angle of slope is the same or nearly so on either side 
(Figs. 237, 238). But a difference of inclination is fre- 
quently to be observed. The Appalachian coal-field, for 
example, as shown by H. D. and W. B. Rogers, presents 
an instructive series of plications, beginning with sym- 
metrical folds, succeeded by others with steep fronts 
towards the west, until at last these steeper fronts pass 
under the opposite sides of the arches, giving rise to a 
series of inverted folds (Fig. 239). 
Fic, 239.—Snc0T1on across THz Forpep Rocks or tun APPALACHIAN CHAIN (H. D. Roars), 

