628 



GEOLOGY. 



and continuations of it. Curved, arched, and contorted stratifications have resulted from 

 the action of the same upheaving cause. Fig. 19. represents an instance of curved strata, 

 as delineated by Dr. Macculloch, occurring in gneiss, at Oreby in the Isle of Lewis, one 

 of the western islands of Scotland. Of the arched form of strata, there are striking 

 examples at Crich-cliff in Derbyshire, at Alum Bay in the Isle of Wight, and in the 



Crich-Hill, Derbyshire. 



Malvern Hills. Fig. 21. exhibits the appearance of contorted strata, as remarked by 

 Murchison on the banks of the Wye. The stratification is said to be unconformable, 

 or discordant, when the planes of the strata in different formations are not parallel to 

 one another, which is usually the case. In Jig. 22. horizontal strata appear divided 



by the inclined, which latter were 

 plainly elevated before the deposi- 

 tion of the former. This is likewise 



- * 2 ' Fl 's- 23 - shown in fig. 23., where, upon a 



base of highly inclined strata, horizontal beds rest, and a series inclined in a different 

 direction. When strata dip in opposite directions, as at a in fig. 24., they are said to 



I form a saddle-back, or anticline ; a word derived from the Greek anti, on opposite sides, 



I and clino, I bend ; and the common ridge from which they diverge is called the anticlinal 



j axis. The hollow formed at b is termed a trough or basin ; the abrupt termination of a 



i series at c is designated an escarpment, bluff, or headland ; a series separated from the 



' main beds to which they belong, as at d, are outliers ; and where a stratum exposes itself 



