Wlarvels of the Universe 1159 
MINERAL OIL 
PETROLEUM, which in its numerous forms has become an indispensable item of domestic and indus- 
trial use, is a mixture of hydrocarbons, whose origin has been variously explained by several opposing 
theories. One view is that it has resulted from the action of water on iron carbide ; another has it 
that carbon dioxide in water has acted on alkali metals in a molten state in an early condition of 
the earth. Others insist that the natural petroleum has resulted from the decomposition of organic 
remains—the animals and plants of the earlier periods represented by the respective geological 
strata from which the oil is now obtained. These strata differ in various parts of the world. In 
parts of America, where the petroleum deposits are so vast that any well sunk into them becomes 
converted into a flowing fountain, the rocks are of Carboniferous, Devonian and Silurian age. The 
outflow from these wells forms lakes of petroleum, as shown in our view of part of the Pearson oil- 
field in Mexico. The deposits appear to be under great pressure from water or gas to cause them 
to rise in such volume wherever a vent is made in the overlying rocks. _ The oil-fields of the Caucasus 
owe their supply to rocks ranging from the Cretaceous to the Miocene periods. The Scotch oils are 
obtained by distillation of carboniferous shales from the Lothians. In this case there is no under- 
ground store of the oil to be tapped ; only by the breaking of the shale into small pieces and their 
subjection to heat can the petroleum be obtained. 
THE AGRICULTURAL ANT, 
The insect to the left is the winged male Ant; in the centre is the large worker; and to the right is a young female. 
THE AGRICULTURAL ANT OF TEXAS 
BY H. ST. J. K. DONISTHORPE, F.Z.S., F.E.S. 
Ir was originally recorded by the ancients that ants stored seeds in granaries to serve as food 
in time of scarcity. This was doubted in the early part of the last century, being regarded 
as a fable or myth. Later, however, the fact was thoroughly re-established, and it is now well 
known that a variety of ants of many different and distantly related genera do harvest seeds 
for food. 
It can be readily understood that in hot, arid countries, where insect food may be lacking, or very 
scarce for many months in the year, and competition with other insect-eaters may also be very keen, 
that it would be of great advantage to ants to become, in part, vegetarians. Moreover, carnivorous 
ants possessing powerful mandibles for crushing the hard integuments of their prey, are well fitted 
to deal with seeds. In many of the harvesting ants, the larger workers, or soldiers, have enormously 
developed heads to support the powerful muscles by means of which their large jaws are worked. 
These workers are literally living “ nut-crackers” for the rest of the community, and they crush 
up the hard seeds when required for food. At the time when these large workers are of no further 
