1881.] 



565 



tions to relate to the navigation of tlie river, because of tlieir situations 

 above, below or at the water level, during the various stages of low. 

 niiclclle or high water. Wherever they occurred at dangerous points, he 

 noticed tliat duplicates were cut so as to face both descending and ascend- 

 ing boats, and the relation of certain marks to safe low water at such and 

 such a point was evident. 



It is probable then that the Bene was used in the pre-Spanish age by 

 the race which has left its noble monuments not only on the plateau be- 

 tween the two Andean ranges, but in the ravines by which the head 

 waters and branches of the Madre de Dios and Bene descend into the 

 plain. He could not find, nor hear of, any architectural remains on the 

 plain itself; but he was informed that a '-fort" stood on an island in a 

 lake which occupies part of the triangle between the Bene on the north- 

 west and the Mamora on the east . 



The plain itself is astonishingly level, the upper reaches of the Bene 

 being only 600 or 700 feet above sea level. [In giving his own exact de- 

 termination from observations with the mercurial barometer (and supple- 

 mentary aneroids) extended through three years at El Paz, he remarked 

 on the falsity of former determinations made during transient stops in 

 the country ; one well known point being put variously from 170 feet be- 

 low, to 1700 feet above tide. This he explained was due to the fact that 

 while the mercurial column is not subject to ordinary fluctuations, and 

 seems for Aveeks at a time to be quite or almost stationary, there is really 

 a steady cyclical rise for six months, and a corresponding steady fall for 

 the other six months of each year, and this must be taken as the basis of 

 all meterological and hypsometrical investigations]. 



Dr. Heath then described in a general way the zoological features of the 

 region ; the abundance of (harmless) alligators in the rivers ; the absence 

 of snakes from the forest plain of inundation, and their presence along the 

 margin of the dry districts ; the wasp-like severity of the bite of the ticks 

 in the forests ; the ii'ritation produced by the abundance of parasitic in- 

 sects on the pampas ; the incredible abundance of bats in the houses, and 

 their thirst for animal and human blood ; the numerous species of 

 monkej^s ; the large size of the cattle of the country south of the Bolivian 

 (east and west) divide ; the change in the voices of birds from hai'sh in the 

 mountain regions to melodious on the plain ; the anvil bird (tree toad ?) ; 

 the organ bird with its diatonic scale of eight ascending notes ; the change 

 of the plumage of paroquets from brilliant varied hues in the northern dis- 

 tricts, to a general pale green in the southern ; the abundance of struthious 

 birds, and the incredible quantity of ant hills in the dry country. 



After various questions asked by tlie members and ^dsitors 

 present, and answered by Dr. Heath, it was, on motion 



Resolved, That the thanks of the Society be tendered to Dr. Heath for 

 his very interesting and important communication. 



