PART I. CHAPTER V. 



69 



Dip and Strike. 



times see the leaves of fossil ferns spread out as regularly as 

 dried plants between sheets of paper in the herbarium of a bota- 

 nist. These fern leaves, or fronds, must have rested horizontally 

 on soft mud, when first deposited. If, therefore, they and the 

 layers of shale are now inclined, or standing on end, it is obvi- 

 ously the effect of subsequent derangement. The proof becomes, 

 if possible, still more striking when these strata, including vege- 

 table remains, are curved again and again, and even folded into 

 the form of the letter Z, so that the 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 bend- 

 ings are repeated four or five times, in the manner represented in 

 Fig 62., the black lines representing 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 deviation from a 



level or horizontal line is 

 called the amount of dip, or 

 the angle of dip. Thus, in 

 the annexed diagram (Fig. 

 63.), a series of strata are 

 inclined, and they dip to the 

 o north at an angle of forty- 

 five degrees. The strike^ or line of bearing, is the prolongation 

 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 

 illustrated 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 strike. 



It is always important for the geologist, who is endeavouring 

 to comprehend the structure of a country, to learn how the beds 

 dip in every part of the district ; but it requires some practice to 



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



