GEOLOGIC WORK OF ANTS—-BRANNER. 313 
ering only the largest and oldest ones made by a single species, and 
found in various different localities, it is noteworthy that there is a 
great difference in the sizes of the largest of them. Just what deter- 
mines this variation I can not say positively, but the influences 
referred to above—that is, rainfall, character of soil, and vegetation— 
naturally suggest themselves as possible influences. 
Nowhere do I remember to have seen more or larger ant hills than 
along Rio Utinga, in the diamond regions of the interior of the State 
of Bahia. From the town Riachao, down the river to the village of 
Pegas, the examples are big and abundant. In a few places they are 
so close together that, big and little, they appear to cover half of the 
ground. My notes, written on the spot, say ‘‘more than half of the 
ground.”” Such places, however, are exceptional. The distribution 
is always more or less irregular—bunched apparently on account of 
characteristics of soil or drainage, or for some other reason that does 
not appear. In some areas of from 10 to 20 acres the ant hills 
occupy from a fifth to a third of the ground, while over larger tracts 
they take up from one-eighth to a seventh of the ground. In height 
the mounds are often as much as 5 meters high, with bases 15 or 16 
meters in diameter. In the forests these mounds are generally over- 
erown with young trees. On many of the big mounds I have seen 
trees more than 30 centimeters in diameter. At the village of 
Antonio Jose the people have planted pineapples upon the mounds. 
At fazenda Bello Horizonte, about 18 kilometers north of the village 
of Pegas, the ant hills are so large and stand so thickly upon the 
ground that they form one of the most striking illustrations I have 
ever seen of the work of these insects. An area of some 30 acres or 
more is there covered with mounds resembling haycocks. They 
probably average 2 meters in height and a diameter of 4 or 5 meters 
at the base. 
At a place called Ponte Nova, on Rio Utinga, 8 kilometers north 
of the village of Pegas, the ant hills are a remarkable feature of the 
landscape. ‘To the east and northeast of the Protestant college the 
mounds cover the old fields. One of the accompanying photographs 
(fig. 2, pl. 1) and text figure 1 were made in this region. 
Six kilometers north of the station one was found by measurement 
to be 1.8 meters high and 4.5+ meters wide at the base. This 
mound was not regarded by the people of the locality as anything 
unusual. e 
To the east of Serrinha several mounds were observed with a height 
of 3 meters and a diameter at the base of 10 meters. These mounds, 
therefore, contain each 78.5 cubic meters of earth. 
Along the western half of the Bahia and Minas Railway, that starts 
from the coast near Caravellas, in the southern part of the State of 
