PLAINS OF THE ELBE, ODER, AND VISTULA. 



305 



hydraulic mucliine. In winter the lakes are covered with ice, and sledges drawn 

 b}^ small horses, ever at a gallop, cross them in all directions. 



But whilst some of the lakes gradually change into rivers, others become con- 

 verted into bogs. This happens mostly in the plains, where the current is 

 sluggish and easily obstructed by vegetation. In so level a country as Branden- 

 burg, Poznania, or Eastern Prussia, the slightest obstacle will cause a river to change 

 its bed. The deserted channel remains behind in the form of stagnant pools and 

 marshes, and in course of time these become filled with peat. This is the origin of 

 the peat bogs of Fehrbellin (which contain many marine plants, and formerly proved 

 a great obstacle to travellers), and of the bogs bounding the chain of lakes traversed 

 by the Havel, which has taken possession of the ancient channel of the Oder. The 

 depression through which the Vistula formerly flowed, when it was still tributary 

 to the Oder, and which is occupied by the Netze and Warthe, is covered with 



Fig. 174. — Diminution in the Volume of the Elbe. 

 According' to Wex. 



reel 

 16-4 



148 

 131 



n-5 



i728 30 40 50 6 1 70 80 90 IJOJ 10 20 30 40 50 60 70 



Mug. Keclll 



swamps only recently drained. An extensive peat bog, known as the Lange 

 Tr'odel, covers the watershed to the east of Bromberg. A bird's-eye view of this 

 country of labyrinthine rivers, swamps, lakes, peat bogs, and vast meadows con- 

 veys the idea of a region recently left dry by a flood. Formerly many of the 

 rivers intermingled their waters. Not two centuries have passed since some of the 

 water of the Vistula found its way into the Upper Oder. The Vistula, when in flood, 

 joined the Ner, a tributary of the Warthe, below Warsaw, and the latter discharged 

 some of its surplus water through the swamps of Obra into the Oder. 



Rivers and Lagoons. 



Nature does not second the efforts of engineers desirous of improving the 

 rivers as navigable highways. Dr. Berghaus proved long ago that the volume 

 of the rivers of Germany has decreased in the course of the last hundred and fifty 



