Position of Strata in Stratified Rocks. 365 



the seams of the strata with the horizon ; the more, on the con- 

 trary, the direction of the section approaches to be perpendicu- 

 lar to that of the strata, the greater will be the inclination of the 

 seams. 



Now, although the position of the strata in a mountain-chain 

 often remain for a great extent of country invariably the same, 

 the varying direction of the accidental sections will make the 

 lines of the stratification appear changing at every step. Hence 

 arises often the mistaken ideas that seems to prevail, that it is of 

 little use to notice, or mark down upon geological maps, the ap- 

 parently too variable position of the strata. While such infor- 

 mation would be of the greatest interest, whenever questions 

 relating to the upheaving of the strata, and of the chain itself, 

 should happen to be examined. 



Of some erroneous opinions to which a neglect of the pre- 

 ceding considerations may have given rise, I shall only notice the 

 following instance. 



It is well known that, at some distance to the south-west of 

 Geneva, the River Rhone makes its way through the Jura chain 

 by a narrow and rocky defile. This pass between the two moun- 

 tains Credo and Varache, is named after the Fort de 1'Ecluse, a 

 small but strong fortress, built in this place, to guard this part of 

 the French frontiers. The direction of the strata of Jura lime- 

 stone, which have been cut through to make way for the river, 

 is nearly north and south, and the direction of the channel in 

 which the river flows nearly east and west ; the dip of the strata 

 is to the east ; and if the two high rocks which form the sides of 

 the channel had been exactly parallel, the direction of this acci- 

 dental section would have shown, on both sides, a similar incli- 

 nation of the seams of the strata corresponding with the dip of 

 the strata themselves to the east. But as the canal is narrower 

 at its eastern extremity than at its western, its two sides are not 

 parallel but converge at the entrance towards the east. Hence 



