Ch. v.] 



DIP AND STRIKE. 



63 



vegetable remains, are curved again and again, and even folded into tlie 

 form of tlie letter Z, so that tlie same continuous layer of coal is cut 

 through several times in the same perpendicular shaft. Thus, in the 

 coal-field near Mons, in Belgium, these zigzag bendings are repeated four 



Zigzag flexures of coal near Mons. 



or five times, in the manner represented in fig. 67, the black lines repre- 

 senting seams of coal.* 



Dip and strike. — In the above remarks, several technical terms have 

 been used, such as dip, the unconformable position of strata, and the 

 anticlinal and synclinal lines, which, as well as the strike of the beds, I 

 shall now explain. If a stratum or bed of rock, instead of being quite 

 level, be inclined to one side, it is said to dip ; the point of the compass 

 to which it is inclined is called the point of dip, and the degree of devi- 

 ation from a level or horizontal line is called the amount of dip, or the 

 Fig. 68. angle of dip. Thus, in the annexed 



diagram (fig. 68), a series of strata 

 are inclined, and they dip to the north 

 at an angle of forty-five degrees. The 

 strike, or line of hearing, is the pro- 

 longation or extension of the strata 

 in a direction at right angles to the dip ; and hence it is sometimes called 

 the direction of the strata. Thus, in the above instance of strata dipping 

 to the north, their strike must necessarily be east and west. We have 

 borrowed the word from the German geologists, streichen signifying to 

 extend, to have a certain direction. Dip and strike may be aptly illus- 

 trated by a row of houses running east and west, the long ridge of 

 the roof representing the strike of the stratum of slates, which dip on 

 one side to the north, and on the other to the south. 



A stratum which is horizontal, or quite level in all directions, has 

 neither dip nor stiike. 



It is always important for the geologist, who is endeavoring to com- 

 prehend the structure of a country, to learn how the beds dip in every 

 part of the district ; but it requires some practice to avoid being occa- 

 sionally deceived, both as to the point of dip and the amount of it. 



* See plan by M. Chevalier, Burat's D'Aubuisson, torn. ii. p. 334. 



