THE FLOODS 243 



of the Bajada is parallel (thirteen days later) to that 

 of Posadas. There is the same parallelism in Novem- 

 ber, December and January. If the summer rains 

 are light on the upper Parana, the flood is late on 

 the lower Parana, and the water is still low there in 

 December (o-20 below the low- water mark on Decem- 

 ber 31, 1910). At the beginning of March, before 

 the maximum of the flood, the curve of Bajada Grande 

 differs from the curve of Posadas. It is the time 

 when the flood of the lower river is caused by the 

 rise of the Paraguay. The secondary floods of June 

 and July again have their origin in the upper Parana, 

 but, as they are added to the flood of the Paraguay 

 on the lower river, they reach a higher level there 

 than at Posadas ; the difference gradually disappears 

 as the flood of the Paraguay subsides. It is the 

 addition of the late floods of the upper Parana to the 

 flood of the Paraguay that causes on the lower river 

 the abnormal floods that occur there at irregular 

 intervals (in 1825, 1833, 1858, 1878, 1905 and 1917). 



Below the Bajada the height of the floods pro- 

 gressively declines. On the estuary they are no 

 longer perceptible ; variations of level are due entirely 

 to the tides. In the channels of the delta of the 

 Parana the tide does not reverse the current as it 

 does in the estuary of the Uruguay, but it causes a 

 slight rise of the water ; and this has been observed 

 sometimes, at very low water, as far as Rosario. 



It is near Corpus, about forty miles above Posadas, 

 that the upper Parana escapes from the restraint of 

 the Brazilian tableland, which imprisons its valley, 

 from the falls of the Guayra, in a deep fissure between 

 lofty basalt cliffs. Below Posadas the river leaves 

 the region of hills and red earth. Below Corrientes 

 it flows everywhere over its own alluvia. Even above 

 Corrientes its form has surprising characteristics of 

 youth. The precise survey done on its banks has 

 brought to light a very distinct break of its fall above 



