CHRONOLOGICAL SUCCESSION OF AQUEOUS ROCKS. 33 



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grouped together under the name of Primary or Palaeozoic, 

 Eocks (Gr. palaios, ancient ; zoe, life), because of the entire 

 divergence of their animals and plants from any now exist- 

 ing upon the globe. The Triassic, Jurassic, and Cretaceous 

 systems are grouped together as the Secondary or Mesozoic 

 formations (Gr. mesos, intermediate ; zoe, life), because their 

 organic remains are intermediate between those of the Pal- 

 aeozoic period, and those of more modern strata. The Eocene, 

 Miocene, Pliocene, and Post-tertiary Eocks are grouped 

 together under the head of Tertiary or Kainozoic Eocks (Gr. 

 kainos, new ; zoe, life), because their organic remains approxi- 

 mate in character to those now existing upon the globe. 



As regards the division of the entire series of stratified 

 deposits into the above enumerated primary " formations," 

 the value of palaeontological evidence has never been dis- 

 puted. In any given country, it would be possible, un- 

 doubtedly, to determine the order and relative succession of 

 the great formations, to some extent at any rate, by a mere 

 appeal to the mineral character and order of superposition 

 of the rocks themselves ; but it is perfectly clear that this 

 method of procedure would necessarily break down totally 

 the moment we came to try and determine what were the 

 corresponding formations in. some far-distant region. By the 

 stratigraphical evidence alone we could determine the relative 

 position and age, for example, of the Silurian, Devonian, and 

 Carboniferous formations in Britain, but it would be an 

 entire impossibility to identify these same formations, say in 

 North America, except by means of the fossils which they 

 contain. So far, then, as this goes, no question has ever been 

 raised as to the value and powers of Palaeontology ; but when 

 we come to consider the minor rock-groups included in these 

 formations, we find much difference of opinion as to the 

 extent to which the evidence of the fossils is available in 

 determining stratigraphical horizons. Part of this difference 

 of opinion is due to imperfect acquaintance on the part of 

 stratigraphical geologists with the methods of palaeontologi- 

 cal inquiry, and needs no discussion here ; but part is well 

 founded, and either arises from actual defects in the modes 

 of research employed by palaeontologists, or is due to the fact 



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