MIGRATIONS. 89 



evitably be some outbreak ; when the rivers can 

 no longer be contained within their natural chan- 

 nel they will overflow, and spread desolation 

 around, till they have passed away and found a 

 place in the great receptacle of waters. Thus, in 

 ancient times, the great northern hive sent forth 

 its numberless swarms, and overturned and di- 

 vided amongst them a considerable portion of 

 that mighty empire which extended its iron 

 sway over the fairest portion of the globe. 1 



With regard to their migrations, animals may 

 be divided into two classes. The first will consist 

 of those that migrate casually, under a certain 

 pressure ; and the second of those that migrate 

 periodically, or at certain seasons. 



1. Of the first description, are those infinite 

 armies of Locusts, which, when they have laid 

 bare one country, as an overshadowing and dark 

 cloud pregnant with the wrath of heaven, pass on 

 to another ; mighty conquerors of old, of whom 

 they were the symbols, from Sesostris to Senna- 

 cherib and Nebuchadnezzar, also mark their pro- 

 gress by devastation and ruin ; to use the graphic 

 language of the prophet " The land is as the 

 garden of Eden before them, and behind them a 

 desolate wilderness . " 2 



This plague has generally been considered 

 as belonging to the old world, in which they 



1 See Appendix, note 19. 



* See on the Locusts Introd. to Ent. 1 Lett. rii. 



