186 



UNCONFORMABLE STRATIFICATION. 



inclined beds (Jig. 297), or where the relative inclination of beds 

 is different, as at a and b (fig. 298), they are said to be uncon- 

 formable. Where a superior deposit, whether stratified or not, 

 rests on a section of the beds of an inferior deposit (fig. 299), there 

 i? a peculiar kind of unconformable stratification, sometimes called 

 transgressive stratification. There is another kind of unconform- 

 able stratification, where the beds are parallel ; this occurs where 

 a horizontal deposit, after having been furrowed in different ways 

 by water, is again entirely covered by a deposit of the same nature 

 which fills up all the excavations (jfig. 300). In this case the 

 strata are unconformable where they join end to end with beds on 

 the slope of ancient valleys. 



Fig. 297. Fig. 298. 



Examples of vnconformable stratification. 



16. To ascertain the relations in the stratification of two deposits, 

 it is necessary to pay great attention to the particular structure of 

 the beds, which in certain cases may lead us into error. For ex- 

 ample, seeing that the divisions of the feed a, (Jig. 301), dip to- 

 wards the left of the figure, we must not conclude that the strati- 

 fication is unconformable with the bed b ; this appearance results 

 altogether from the structure which the bed a owes to its rapid 

 formation under particular circumstances. (See page 138.) 

 Fig. 301. Fig. 302. 



Examples of doubtful stratification. 



17. Schistose substances often present many difficulties, in this 

 respect, because their divisions run in every direction, and some- 

 times the least apparent is the real stratification. For instance, we 

 might suppose the deposit a, (Jig. 302), rested conformably on the 

 deposit 6, and that the mass c is an unconformable stratification, from 

 regarding the finest divisions of the schist as indicative of the stra- 



16. What is meant by doubtful stratification 1 



17. What is false stratification? 



