CONDITIONS OF SEDIMENTARY DEPOSITION. 489 



thetical. An existing case, which approaches the conditions 

 assumed by Babbage, is that of the Rio Uruguay, which is 

 described by Revy. 1 



" The little town of Higueritas, also called Nueva Palmira, 

 is situated in latitude 33°52'S. f long. 58°23' W., in the Banda Ori- 

 ental, at the junction of the Uruguay with various branches of the 

 Parana, all of which discharge jointly their volume into the La 

 Plata. Three miles below Higueritas, at Punta Gorda, the La 

 Plata proper commences ; three miles above Higueritas the 

 Uruguay opens into a lake from 4 to 6 miles wide and about 56 

 miles long. There are no islands on this lake, although, with 

 the exception of a deep channel half a mile wide of steep sides 

 and submerged, the lake is shallow ; it may be called the estuary 

 of the Uruguay. A little a£>ove Fray Bentos, 58 miles from Hig- 

 ueritas, the first islands appear within the lake ; and, their num- 

 ber soon increasing, we enter the delta of the Uruguay, which for 

 25 miles more retains the width of the lower lake, breaking, 

 however, up into a great number of large and small islands, until, 

 a little below Paysandu, the river proper commences within a con- 

 fined channel. At Paysandu, a commercial town of importance, 

 125 miles from Higueritas, the delta of the Uruguay commences. 

 At Fray Bentos the visible delta terminates ; and from the latter 

 place to the La Plata the future delta of the Uruguay is now in 

 course of formation 



.... During the survey of the Uruguay there was a period- 

 ical rise of the river, viz., on February 3, 1871, and a sample of 

 water was taken on that day at the Salto section, about 200 

 miles above Higueritas. The water was turbid, of deep brown 

 color ; and the analysis of the sample showed that it contained 

 one part by weight of solid matter in suspension in 9524 parts of 

 water. There was no perceptible change in the color of the 

 water or in its analysis, until we reached Fray Bentos [142 miles 

 below Salto] on the 5th February, 1871, and here it contained 1 

 part solid matter in 1 1,200 of water by weight in suspension. At 

 Higueritas, on the same day, the waters of the Uruguay ap- 



1 Hydraulics of Great Rivers. J. J. Revy, pp. 134-135. 



