TIIE HUMAN SPECIES. 129 



state.* 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 conse- 

 quence of the igneous exhaustion of that region producing a 

 considerable 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 maimer on 

 the Rhine, & ise, I Sch* 1 It. But th — Important altera- 

 tions in N\ 1 1 nnany 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 at Arend See, in Brandenburgh, 

 a lake of about sixteen square miles' surface, apparently pro- 

 duced 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 16G0. 

 It is one of the same class as that subsidence of the earth, 

 which occurred in 1806, near the delta of the Indus. 



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 period, covered the drainage of the Elbe, the 

 Weser, and the Ems, &cc, more anciently communicating, but 

 imperfectly, with the Gallic Sea, (perhaps at high water only, 

 through the Belgian low lands, behind the chalk cliffs of the 

 coast to the Liane, south of Boulogne,) suddenly forming a 



* We have picked up oa the German side of the Rhine, near Wezel, 

 6everal univalves, and a pinna, with the hinge ending in a very acute 

 point. These were found on the line of the new chaussce. 



