III. MESOZOIC TIME. 



Mesozoic or mediaeval time in the earth's history comprises a single era 

 only. It is the era of the Secondary formations of early geological science, 

 and that of the Reign of Reptiles of Agassiz. 



It is remarkable as the era of the culmination and incipient decline of 

 three great types in the Animal Kingdom, the Amphibian, Reptilian, and 

 Moliuscan, and of one in the Vegetable Kingdom, the Cycadean. It is also 

 remarkable as the era of the first Mammals, of the first Birds, of tlie first of 

 the Common or Osseous Fishes, and of the first Palms and first Angiosperms. 



Subdivisions. 



3. Cretaceous Period, W. H. Fitton, Ann. Phil, 2d. Ser., viii., 382, 1824. 

 The Chalk Period, or the period of the Chalk formation. 



2. Jurassic Period, A. Brongniart, Tabl. des Terrains, 221, 1829, the name 



referring to the Jura limestone and other related beds of the Jura 

 Mountains between France and Switzerland, 



1. Triassic Period, F. v. Alberti, Beitrag Mon. d. hunten Sandsteins, 



Mitschelkalks u. Kenpers, Stuttgart, 1834, — the name, from the Latin, 

 referring to a threefold division of the formation in Swabia, Franconia, 

 and Lorraine. Variegated sandstone. Buntersandstein, this German 

 name used for part of the strata by Werner. Poikilitic group (Poecilitic) , 

 Conybeare and Buckland (from the Greek, Trot/ctAos, variegated) , Back- 

 land's Bridgeivater Treatise, ii., 38, 1836. New Red Sandstone group or 

 formation, Lyell, El. of Geol, 1833, 1842 — Mercian of T. McK. Hughes 

 = Triassic + Jurassic. 



The Triassic and Jurassic rocks in some regions make together a continu- 

 ous series, not easily separated, and the formation is then often called the 

 Jura- Trias. 



The generally accepted subdivisions of the three periods are the 

 following: — 



3. Cretaceous : (1) Lower ; (2) Upper. 



2. Jurassic : (1) Lower, or Liassic (from the Lias, of England) ; (2) Middle, 



or Oolytic (from the oolitic character of some of the limestones 

 in England) ; (3) Upper, or Portlandian (from the Portland beds in 

 England) . 



1. Triassic: (1) Lower Trias, or Vosgian (from the Vosges Mountains); 

 (2) Middle Trias, or Franconian (from Franconia in Germany) ; (3) 

 Upper Trias, or Keujoerian (from the name Keuper in Germany) ; 

 (4) Rhcetic (from the Rhaetian or Tyrolese Alps). 



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