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great masses of mountains into several chains, 

 merits particular consideration with respect to 

 the height more or less considerable of the bottom 

 of the inclosed basins, or longitudinal vallies. 

 Geologists have hitherto been much more oc- 

 cupied by the successive narrowing of these 

 basins, their depth compared with the walls of 

 rock that surround them, and the correspondence 

 between the re-entering and saliant angles, 

 than by the level of the bottom of the vallies. 

 No precise measure yet indicates the absolute 

 height of the three basins, of Titicaca, Jauja, 

 and the Upper Maragnon * ; but I was fortu- 

 nate enough to be able to determine the six 

 other basins, or longitudinal vallies, which suc- 

 ceed each other, as by steps, towards the north. 

 The bottom of the valley of Cuenca, between 

 the knots of Loxa and Assuay, is 1350 toises ; 

 the valley of Alansi and of Hambato, between 

 the knot of the Assuay and the ridge of Chi- 

 sinche, 1320 toises ; the valley of Quito -f- in 



* I am inclined to believe that the southern part of the 

 basin of the Upper Maragnon, between Hilary and Huacara- 

 chuco, surpasses at least 350 toises ; for I found the mean 

 waters of Maragnon, near Tomependa, 194 toises above the 

 level of the Ocean ; and, according to the analogy of the 

 course of the Magdalena, between Neiva and the Angostura 

 of Cavare, the Upper Maragnon, may in a course of 4° of 

 latitude, have a fall of 150 toises. 



t The valley of Quito, I naquito, and Turubamba, ought to 



