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 A?'cheozoic, from 

 the Greek for bcgiiuiing 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, In- 

 sects, Fishes and Reptiles existed. It includes three Ages : (i), the 

 Silurian; (2), the Devonian, or Age of Fishes ; and (3), the 

 Ca7'boniferoiis, or Age of Coal-plants, when the most extensive 

 beds of mineral coal of the world were originated. 



2 Mesozoic time, or ih^t oi medieval life. It corresponds to 

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

 that of their chmax 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. 



Cenozoic time is divided into two Ages, the Tertiary and the 

 Quaternary. The Quaternary age, the last in the geological 

 series, commences with the Glacial period, when, over Northern 

 North America, vast quantities of stones, gravel and sand, were 



Y 



