DIFFERENT KINDS OF STRATIFICATION. 18A 



stratification : one horizontal (which is the natural stratification), 

 according to which all transported matters are de-posited under 

 water; the other more or less inclined, resulting from upheavals 

 which have taken place at different epochs. In the latter we dis- 

 tinguish the degree of inclination, or dip, which may be vertical, 

 and the point of the horizon towards which the beds dip. The 

 last part of the observation determines the direction of the crests of 

 the strata, or, as we say, the strike or direction of the strata, which 

 i? always at right angles to the dip or direction of the inclination, 

 and which also indicates the direction of the movement by which 

 the effect was produced. But the first observation of horizontal, or 

 inclined strata, is not always sufficient ; it is frequently necessary 

 to distinguish the relative stratification of different deposits, which 

 is reduced to the concordance or the discordance which may exist 

 between them. 



13. The dip of strata is the point of the compass towards which 

 they slope, while the angle they form with the plane of the horizon 

 is called the angle of dip. The term dip refers to the inclination 

 of a stratum, and the term strike is used to express its direction. 

 Thus, strata may dip to the north at an angle of forty-five degrees ; 

 in this case, the strike, or line of bearing, must necessarily be east 

 and west, because the strike is always at right angles with the dip. 



* Dip and strike may be aptly illustrated by a row of houses run- 

 ning 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." The angle formed by the roof 

 with the plane of the horizon would be the angle of dip. 



14. Conformable stratification. When all the strata of a forma- 

 tion are parallel to each other, that is, when there is a concordance 

 between them, whatever may be their general position, horizontal 

 or inclined, convex or concave, they are said to be conformable 

 (figs. 293 to 296). 



Fig-. 293. Fig-. 294. Fig-. 295. Fig-. 296. 



Different, kinds of conformable stratification. 



15. Unconformable stratification. When the strata of a forma- 

 tion are not parallel to each other, when there is a discordance 

 between them, as where horizontal strata come in contact with 



13. What is meant by the dip of strata? What is the angle of din? 

 What is meant by the term strike ? 



14. What is meant by conformable stratification ? 



15. What is meant by unconformable stratification 7 Is it always of the 

 amc character? 



16* 



