184 RELATIVE AGES OF DEPOSITS. 



live ages by their number in the order of succession ; the deepest 

 being the most ancient, arid that forming the surface being the most 

 modern. It would then be sufficient, in sections of different depths 

 which would be found elsewhere, to count from above downwards, 

 to know always where we were, and even the variations that a 

 determinate bed might undergo in different places would offer no 

 difficulty to observation. But such is not the case ; the numerous 

 escarpments we meet, always present us with but a very small 

 portion of .the series, sometimes in one part of its thickness, and 

 sometimes in another ; we never see the entire series ; and il is 

 only by combining the observations made in different places, that 

 we have been able to establish what we now know, at the same 

 time we discovered the particular circumstances of formation of 

 each deposit. 



In consequence of the divisions of the whole, it is conceived, it might be- 

 come very difficult to distinguish them, and that in presence of an escarp 

 ment one might frequently be unable, at first sight, to decide on the point in 

 the series to which it ought to bo referred. Indeed, different beds of the 

 same nature which succeed each other in the series, are often very analogous, 

 the limestones of one story more or less resembling those of another ; and 

 the same is true of different deposits of sandstone and clay. It also happens 

 that the same deposit varies at different points : here it is a compact, and 

 there, an earthy limestone ; in another place the same limestone is found 

 mixed with sands, and, further on, it is nearly pure sand, &c. The injection 

 of crystalline matter adds to the embarrassment, by the modifications it 

 causes in the texture, and even in the nature of everything in its vicinity. 

 It is also conceived, that the fewer the beds superposed in the same place, 

 the greater the difficulties, and they are at a maximum when we meet an 

 isolated deposit, without knowing on what it rests, arid not being able to 

 perceive anything it covers : this occurs in a great many countries. It 

 often happens, too, that one or more beds are entirely wanting in one loculi- 

 ty, and then the deposits which should naturally separate them, being im- 

 mediately superposed, exposes the observer to attribute to the succeeding 

 beds an age very different from that which really belongs to them. 



11. To obviate this difficulty, we have observations on the con- 

 tinuity of beds, some of which we can follow from points where 

 they present certain characters, to others where they offer different 

 characters; from points where they are entirely isolated, to others 

 where we can see on what they rest, and what covers them, &c. 



We have also observations on stratification and inclination of different 

 beds towards one point or the other, which enable us to infer that such a 

 species of deposit passes below or above another, found isolated or at a dis 

 tarice. Fragments and rolled flints may evidently indicate the priority of 

 deposits which contain them, to those from which they came, and thus fur. 

 nish a good means of distinction, when they are sufficiently characterized. 

 And the nature of organic remains has now become a very decided aid in 

 distinguishing different formations. 



12. Different kinds of stratification. There are two kinds of 



11. How are we enabled to judge of the relative ages of deposits? 



12. How many kinds of stratification are described ? What is observed 

 in .nclined stratification? 



