30 ■ 



rock is formed by compact sand stone covered by 1,50 me- 

 ters of sand. This rock has a depression which follows the 

 very thalweg of the river, allowing' therefore the dredging 

 of a channel with 9 feet of depth with exception at the 

 one place, where sand stone is found at a depth of 

 2,32 meters. 



A little above this bar, the depression formed in the 

 hard sandstone seems to divide itself in a direction towards 

 the Argentine coast in front of the arroyo «Mellado», 

 passing between two banks formed by sand and gravel. 



Even if it were true that this depression continued till 

 the curve of 3 meters depth, ( which however is not likely 

 to be the case ), it is believed that a channel cut in this di- 

 rection would be difficult to maintain, as it is situated be- 

 tween banks, the dimensions of which have augmented con- 

 siderably as appears from a comparison of the figured plans 

 of 1890 'and 1900. 



The contrary is observed in the channel passing the 

 middle of the river, and as the bank in front of the island of 

 Chapicuy » has disappeared, there is reason to believe that 

 once, when the bar of sand stone in the extreme south of 

 The channel has been levelled, the result of this work will 

 be the absolute maintenance of its upper part, the more so 

 as the projected direction corresponds exactly with the 

 thalweg, which form corresponds to the layer of sandstone. 



As for the other project in the direction O. P., though 

 its upper mouth would have the advantage of being better 

 defined, I he borings have shown the ground to be impene- 

 trable to the boring tool at a depth less than ±74 meters, 

 reason for which the acceptance of this direction must be 

 rejected. 



'fhr channel was therefore projected in the middle of 

 the depression, which is impenetrable to the boring tool, 

 but the curve of the channel makes it necessary to increase 

 its width to 80 meters. 

 CompaI [t is very useful to compare the cube necessary to be ex- 



bet drr«tio h n e s! w ° cavated for a curved as well as for an absolute straight 

 channel which unites the curves of 8,00 meters depth and 

 w Inch therefore is done below : 



