^6 CHARLES LAURENCE BAKER 



from north of Porto Tibiriga to the falls of La Guayra or Sete 

 Quedas, for a distance of 250 miles or more, these sandstones have 

 strongly incHned bedding, very delta-like in nature, dipping in the 

 direction of the flow of the river. Should one make the error of con- 

 sidering these sandstones originally deposited horizontally and later 

 tilted, he would compute their thickness in many thousands of feet. 



The Parana River flows in a canyon with walls of soHd basalt 

 all the way from the falls of La Guayra or Sete Quedas, to a point 

 12 miles below the city of Posadas, territory of Missiones, Argentina, 

 a straight line distance of nearly 250 miles. The breadth of the river 

 just above La Guayra Falls is 12,600 feet and its mean depth at 

 low water is perhaps 3 feet. The breadth of the river at the foot 

 of the falls is 262 feet. The height of the uppermost (lowest) fall 

 is 50 feet, but there are eighteen different groups of faUs around 

 both sides and at the head of a narrow trench incHned downstream, 

 and 10,750 feet in length. For 100 miles below the present falls 

 there is a difference of 100 feet below high- and low-water levels in 

 the river. The river falls 373 feet in the distance of 40 to 45 miles 

 between the head of the falls and Porto Mendez.^ There is a strong 

 gradient in the river all the way from the latter place to within 

 25 miles of Posadas, at which place a cross- syncline in the basalt 

 brings the supra-basalt formation down to the low-water level. 

 With this exception the entire gorge of the river between La Guayra 

 Falls and a point 12 miles below Posadas is cut through very 

 resistant solid basalt, and at no place is the base of the basalt 

 exposed, although possibly some important undermining action 

 has taken place under the low-water surface. Not only are the 

 falls of La Guayra the mightiest in volume in the world, but they 

 are one of the oldest, if not the very oldest, known. 



The lowest or great falls of the Iguassu River, now situated 

 1 2 miles above the confluence of that river with the Parana, have a 

 mean fall of about 230 feet, all through soHd basalt. The great 

 Iguassu Falls are said to have a volume greater^ than those of 



' The writer is indebted for these data to Mr. Wilson Sidwell, C.E., who has made 

 the only accurate survey of the falls. 



= Probably overestimated, at least as respects mean flow. 



