APPENDIX. 



The following brief explanations are here added for the benefit of the 

 general reader. 



I. GEOLOGICAL TIME. 



The terms Paleozoic era, Oolitic period, and Glacial era or period 

 have been used in the preceding pages. The positions of these eras in 

 geological history, will be gathered from the following review of its 

 principal divisions. 



Geological history begins with what has been called Azoic time, azoic 

 signifying the absence of all life. But the rocks supposed to be Azoic 

 have been found to afford evidence of the existence of the simplest kinds 

 of life during their formation ; and the era they represent, is, therefore, 

 more correctly styled the Archeozoic, from the Greek for beginning and 

 life. 



The other grand subdivisions of geological time, are as follows : 



Paleozoic time (named from the Greek for ancient life), in the course 

 of which the earliest Corals, Mollusks, Crustaceans, Insects, Fishes and 

 Reptiles existed. It includes three ages : (1), The Silurian ; (2), the De- 

 vonian, or Age of Fishes ; and (3), the Carboniferous, or Age of Coal- 

 plants, when the most extensive beds of mineral coal of the world were 

 originated. 



2. Mesozoic time, or that of mediaeval life. It corresponds to the 

 Age of Reptiles — being the era, not of the earliest reptiles, but that of 

 their climax in number, size and variety. This age is divided into three 

 periods : first, or earliest, the Triassic ; second, the Jurassic, to which the 

 Oolitic era belongs ; and, third, the Cretaceous, or that of the Chalk. 



3. Cenozoic time, or that of recent life, as the term signifies. It 

 is modern in the aspect of its species, compared with the Mesozoic, and 

 still more so compared with the Paleozoic. The highest and dominant 

 species were Mammals, ending in Man. 



