PART I. CHAPTER V. 



71 



Dip and Strike. 



Fig. 65. formed by the meeting of the hands, 



so as to give an angle of 45, or 

 whether it would divide the space 

 into two equal or unequal portions. 

 The upper dotted line may express 

 a stratum dipping to the north ; 

 but should the beds dip precisely to 

 the opposite point of the compass 

 as in the lower dotted line, it will 

 be seen that the amount of incli- 

 nation may still be measured by 

 the hands with equal facility. 



It has been already seen, in de- 

 scribing the curved strata on the 

 east coast of Scotland, in Forfarshire and Berwickshire, that a 

 series of concave and convex bendings are occasionally repeated 

 several times. These usually form part of a series of parallel 

 waves of strata, which are prolonged in the same direction 

 throughout a considerable extent of country. Thus, for exam- 

 ple, in the Swiss Jura, that lofty chain of mountains has been 

 proved to consist of many parallel ridges, with intervening lon- 

 gitudinal valleys, as in Fig. 66., the ridges being formed by 



Fig. 66. 



Section illustrating the structure of the Swiss Jura. 



curved fossiliferous strata, of which the nature and dip are occa- 

 sionally displayed in deep transverse gorges, called " cluses," 

 caused by fractures at right angles to the direction of the chain.* 

 Now let us suppose these ridges and parallel valleys to run north 

 and south, we should then say that the strike of the beds is 



* See M. Thurmann's work, " Essai sur les Soulevemens Jurassiques du Por- 

 rentruy, Paris, 1832," with whom I examined part of these mountains in 1835. 



