26 GEOLOGICAL BIOLOGY. 



2. Upper Helderberg ) 



Period } ist epoch. Schohane grit, etc. 



3. Hamilton Period. ... 1st epoch. Marcellus shales, etc. 



4. Chemung Period 1st epoch. Portage, etc. 



5. Catskill Period.. . i CatS "? sandstone a "d 



( shales, etc. 



III. Carboniferous Age. 



1. Subcarboniferous ) . ^ 



Period f ist epoch. Conglomerates, etc. 



2. Carboniferous Pe- ) 



rioc j } ist epoch. Millstone grit, etc. 



3. Permian Period, etc. 



This classification was further elaborated in his manual, 

 the first edition of which appeared in 1863,* and it has become 

 the standard classification for American geology. Here we 

 find the larger divisions, called times : I, Archean ; II, Palae- 

 ozoic; III, Mesozoic; and IV, Cenozoic times. The Palaeo- 

 zoic time is classified into ages, viz. : The age of Invertebrates, 

 the Cambrian and Silurian; the age of Fishes, the Devonian; 

 the age of Coal Plants, the Carboniferous. The Mesozoic is 

 called the age of Reptiles. The Cenozoic time includes the 

 age of mammals and the age of man.f 



Each of the ages is subdivided into periods and epochs, in 

 which the stratigraphical groups and formations form the 

 basis, and the particular faunas and floras of each constitute 

 the data of determination for the time-divisions. 



The following chart shows the modifications in the nomen- 

 clature through which the classification now in use has grown 

 out of the classifications of earlier authors : 



* James D. Dana, " Manual of Geology; treating of the principles of the 

 science, with special reference to American Geological History," ist edition, 

 1862 ; 2d edition, 1874 ; 3d edition, 1880 ; 4th edition, 1895. 



f In the article of 1856 the following periods were named (i.e., Triassic, 

 Jurassic, Cretaceous, Tertiary, and Post-tertiary), but divisions into epochs 

 were in this paper proposed only for the latter. The divisions of the Post- 

 tertiary were the Glacial Epoch, the Laurentian Epoch, and the Terrace Epoch. 

 Quaternary has been substituted, in the manual for Post-tertiary, and Champ- 

 lain epoch for Laurentian. 



In the last edition (1895) Era has taken the place of Age in the former 

 editions, a Cambrian Era has been recognized in addition to Lower Silurian, 

 and Carbonic Era has been substituted for Carboniferous Age ; the name 

 Carboniferous being applied to the formations included under the terms Coal- 

 measures and Millstone grit of the early classifications. 



