THE HUMAN SPECIES. 59 



No extensive deposits, brought by lengthened water 

 courses, had as yet formed deltas ; for, while the great 

 volcanic craters from the Vogesian chain to Kloster 

 Laach, in the basin of Neuwied ; of the Pulvermar, 

 near Gillenfeld, in the Eifel, &c., were in activity, the 

 Rhine had not broken through in a northern direction ; 

 and the event may be regarded as a consequence of 

 the igneous exhaustion of that region producing a con- 

 siderable change in the levels. The same law which 

 altered successively the courses of the Oxus and the 

 Jaxartes towards the north, may have operated, in a 

 similar manner, on the Rhine, Meuse, and Scheldt. 

 But these important alterations in Western Germany 

 and Gaul, were effected, and their consequences were no 

 doubt considerably advanced, before man was present 

 in Europe ; yet comparatively recent the period may 

 be deemed, since the Arend See, in Brandenburgh, a 

 lake of about sixteen square mile's surface, apparently 

 produced by subterraneous percolation, which causes 

 the earth to sink vertically, in stages each of about 

 forty feet perpendicular, offered a further instance of 

 this phenomenon so late as 1660. It is one of the same 

 class as that subsidence of the earth, which occurred 

 in 1806, near the delta of the Indus. 



1 With the prolongation and change of direction in the 

 course of the rivers in Western Germany, the weight 

 of waters, or a contemporaneous percussion, may have 

 shaken the chalky and alluvial shores, converting 

 Britain from a peninsula into an island, and forming 

 the Channel and Dover straits. Waters which, until that 



