ORDER OF STRATA. 



mations that we find the remains of the different organized bodies 

 by which the earth has been successively peopled. 



28. These stratified formations were not all produced at once, 

 but successively, and under the influence of different circumstances; 

 they constitute, as we have before said, distinct beds or strata, 

 and these strata lie one on top of the other, so that those of a more 

 ancient are found beneath those of a more recent formation. By 

 studying them carefully we shall also perceive that different points 

 on the surface of the earth have been successively, and at intervals, 

 left dry, and covered by the waters of the sea, or by fresh water, 

 the sediment from which constitutes these banks, and we see that 

 these banks themselves differ, not only in the nature and disposi- 

 tion of their constituting elements, but also in the nature of the 

 remains of the organic bodies buried in their substance. 



29. We distinguish a great number of these stratified forma- 

 tions, and, as might be anticipated from their mode of production, 

 they are everywhere found in the same order of superposition ; 

 the formation which, in one locality, covers another formation, can 

 never be found in another place beneath the latter; it may be 

 entirely wanting, so as to leave the latter uncovered, or in contact 

 with a stratum, which in another place it covered ; but wherever 

 it exists, it must be on top of or superior to all formations, the pro- 

 duction of which dates back to a more remote epoch. 



80. For example, we have stated that in the vicinity of Paris, the 

 gypsum rests upon the coarse limestone, this upon the plastic clay, 

 and this plastic clay upon the chalk ; in other localities we^ may 

 find new strata interposed between these various formations, or we 

 may find one of them entirely wanting ; for example, the plastic 

 clay being absent, the coarse limestone would be found resting 

 directly upon the chalk ; but this coarse limestone, for the reason 

 alone that it is everywhere found resting upon the chalk, must have 

 been deposited after the chalk was formed, and consequently can 

 never be found below it. 



31. It is also evident that when these solid beds are slowly 



Sea. 



Sedimentary Rocks. 

 Plutonic Rocks. 

 Fig. 1. 



28. Were the stratified formations all produced at the same time ? Are 

 all the stratified rocks alike in character ? 



29. Are the stratified formations always found in the same order of sue- 

 .ession ? Are all the strata everywhere found ? 



30. Give an example to show that the strata are always found in the sama 

 order of succession. 



31. What is the position of sedimentary rocks ? 



