538 Heath's Bolivian Explorations. [September, 
flowing in from the north, to which he gave the name of 
Orton, in honour of the celebrated explorer. The land in 
this vicinity is low and marshy, with few trees. At midday 
he found a porpoise, which accompanied him all that day 
and a part of the next, until he came to the upper Rapids 
just above the Falls. The appearance of this porpoise gave 
him great encouragement, as the Madeira and Mamore 
Rivers are full of porpoises, but the Beni has none. It was 
an indication that there were no dangerous Falls below him. 
During the day the Tabanos, a horse-fly, both yellow and 
black with white-tipped wings, disappeared, and myriads of 
sand-flies took their place. These sand-flies are found on 
all the tributaries of the Amazon, and Humboldt estimated 
that on the Orinoco there are a million of these flies to every 
cubic foot of air. There are two species of these sand-flies, 
called Pium and Maruim, differing only in size. During 
the night, while the Doctor was taking an observation with 
his sextant, the mosquitoes alighted on his face in such num- 
bers that the blood trickled down on his garments. They 
got into his eyes, and alighted on his mercury, and disturbed 
his mercurial horizon to such an extent that he could not 
take his usual observation. The burning of the Pampas 
had so filled the atmosphere with smoke that he was com- 
pelled to work his artificial horizon without its usual glass 
cover, and stars of the first magnitude appeared as dim as 
those ordinarily of the fourth and fifth magnitude. The 
change from the Tabanos to the Maruims caused him to 
remember that the same change took place on the Mamore 
just above the Falls, and he believed he was approaching 
the Falls corresponding to the same point in the Mamore. 
In the distance he saw tapering columns of smoke escaping 
from the leafy roof of the forest, which probably curled up 
from fires burning at Indian camps beneath. 
The next day the DoCtor saw two turkeys on the bank, so 
tame that he shot one, and re-loaded and shot the other 
while it stood looking at its fallen companion. The same 
day he passed two large islands, and at 10 o’clock in the 
morning he reached a point where the river was obstructed 
by rocks, forming a rapid current, which he passed without 
difficulty, and soon afterward reached the main Falls. 
Failing to find a suitable passage for his boat on the north 
side, he passed over to the south side of the river, where he 
succeeded in drawing the boat over the rocks to the waters 
below. The difference of level between the water above and 
below the Falls is 28 feet, the angle of descent of the water 
in the main shoot is 25 degrees, and the falling water points 
