180 PRINCIPLES OF CLASSIFICATION [Cu. XIII 



formabiy on the older set. There may even be a blending of the 

 materials constituting the older deposit with those of the newer, so 

 as to give rise to a passage in the mineral character of the one rock 

 into the other as if there had been no break or interruption in the 

 depositing process. 



Although by the frequent discovery of new sets of intermediate 

 strata the transition from one type of organic remains to another is 

 becoming less and less abrupt, yet the entire series of records appears 

 to the geologists now living far more fragmentary and defective than 

 it seemed to their predecessors half a century ago. The earlier en- 

 quirers, as often as they encountered a break in the regular sequence 

 of formations, connected it theoretically with a sudden and violent 

 catastrophe, which had put an end to the regular course of events 

 that had been going on uninterruptedly for ages, annihilating at the 

 same time all or nearly all the organic beings which had previously 

 flourished, after which, order being reestablished, a new series of events 

 was initiated. In proportion as our faith in these views grows weaker, 

 and the phenomena of the organic and inorganic world presented .to 

 us by geology seem explicable on the hypothesis of gradual and in- 

 sensible changes, varied only by minor convulsions, such as have been 

 witnessed in historical times ; and in proportion as it is thought possi- 

 ble that former fluctuations in the organic world may be due to the 

 indefinite modifiability of species without the necessity of assuming 

 new and independent acts of creation, the number and magnitude of 

 the gaps which still remain, or the extreme imperfection of the record, 

 become more and more striking, and what we possess of the ancient 

 annals of the earth's history appears as nothing when contrasted with 

 that which has been lost. 



When we examine a large area such as Europe, the average as well 

 as the extreme height above the sea attained by the ol$er formations 

 is usually found to exceed that reached by the more modern ones, the 

 primary or paleozoic rising higher than the secondary, and these in 

 their turn than the tertiary, while in reference to the three divisions 

 of the tertiary, the lowest or Eocene group attains a higher summit 

 level than the Miocene, and these again a greater height than the 

 Pliocene formations. Lastly, the post-tertiary deposits, such, at 

 least, as are of marine origin, are most commonly restricted to 

 much more moderate elevations above the sea level than the tertiary 

 strata. 



It is also observed that strata, in proportion as they are of newer 

 date, bear the nearest resemblance in mineral character to those which 

 are now in the progress of formation in seas or lakes, the newest 

 of all consisting principally of soft mud or loose sand, in some places 

 full of shells, corals, and other organic bodies, animal or vegetable, in 

 others wholly devoid of such remains. The farther we recede from 

 the present time, and the higher the antiquity of the formations which 

 we examine, the greater are the changes which the sedimentarv de- 



