FEB. 1911.] NAKANO—THE VEGETAT. OF LAKES AND SWAMPS. 39 



In the following lines I shall try to give a brief account 

 about the origin of the swamp. For this evidence we may- 

 point out the following facts : — 



a). The swamp has the form of a very long crescent, its 

 axis running parallel to the course of the Tone, and its depth 

 being rather uniform. 



b). The eastern part is still connected with the river, and 

 it may be well conjectured by the observations of the topo- 

 graphy in this district, that in old ages, the western valley of 

 the swamp was connected with that of the river. 



From these it is sufficient for us to imagine that the valley 

 of the swamp is the cutt-ofif part of the meandering course of 

 the river. Besides these we may enumerate another evidence 

 of the river-origin of the swamp. 



The place near the swamp and its vicinity suffer an inunda- 

 tion every year, since the River '' Kinu " which collects the 

 vsrater of the mountaineous districts of Nikko flows into the 

 Tone at a point about five miles west apart from the swamp. 

 When heavy rain in summer last for many days the Tone 

 rises and flows over cultured fields. So even in the present 

 day, change of the river course is likely to occur when it is not 

 prevented by artificial works. 



Also we find many river-relic-swamps of a smaller scale in 

 the bank of the river, for example, in a pool between the village 

 *' Nakabyo " and islet " Chobetsu." The western part of the 

 pool was buried by a sandj^ deposit while the eastern part 

 still connects with the river through a small brooklet. 



From an old record^^ we know that in old times the River 

 Kinu combined with the River Kokai flow^ed into the River 

 Tone. It may, therefore, be well inferred that in former ages, 

 the current of the Tone along this district was stronger than 

 in the present. 



Taking all the above cases into consideration, it may not 

 be too bold to conclude that the Tega-swamp was formed 

 through the change of the course of the Tone. 



1) SoTAN Akamatsu: Pictorial records of ti:e Eiver Tone. 



