MINERAL OIL 
203 
acres at Moreni has yielded over 52,500 barrels per acre. 
Some Roumanian upfolds have been broken through by 
rising cores of rock and salt-domes (Fig. 55). 
Asia—Cavcasus, PErsia, BurMA, EASTERN ARCHIPELAGO 
—The Baku field, W. of the Caspian and S. of the Caucasus, 
has yielded oil and natural gas throughout historic times. The 
oil comes from Pliocene, Miocene, and Oligocene sands which 
occur as lenticles in clay. The beds have been folded and 
the main supplies, as from Bibi Eibat, are from anticlines. 
Some wells must draw their oil from a large area, for one plot 
of 27 acres in that field has yielded in 36 years 2,200,000 
barrels of oil per acre, or sufficient to cover the ground to 
a depth of 286 feet (Beeby Thompson, Oil Field Exploration, 
i, 1925, p. 335). The surface is largely occupied by barren 
freshwater sands, which overlie the Lower Pliocene oil 
sands; they rest upon the Spirialis beds from the abundant 
organic matter in which the oil may be derived. In the 
Caucasus other oil supplies came from Miocene and Oligo- 
cene beds, which include lacustrine and marine shales rich 
in diatoms, fish, and mollusca. The Baku field has hitherto 
been the most prolific oilfield in the Old World. 
The Persian and Mesopotamian oilfield lies along the fold- 
mountains of the Persian Arc, which runs from near the 
Caspian through South-western and Southern Persia till it 
rejoins the axis of the Alpine-Himalayan System in North- 
western India. The Cretaceous rocks include many gash 
veins, and according to one hypothesis the oil has risen from 
the Mesozoic limestones into the porous beds of the Miocene 
Asmari Limestone, which is the chief reservoir of oil. This 
theory of migration offers an explanation of the high quality 
of the Persian oil. According to the alternative hypothesis 
the oil was formed from the organic matter deposited under 
lagoon conditions in the Asmari limestones. 
In South-eastern Asia a loop from the Himalayan System 
traverses Western Burma and passes along Sumatra, Java, 
and the southern side of the Eastern Archipelago. This 
Burmese-Malayan Arc includes several important oilfields. 
The Burmese oilfield lies beside the Irrawadi in rocks ranging 
from the Cretaceous to the Pleistocene. The main oil 
supply is in the Pegu beds (Oligocene to Miocene) ; they 
consist of marine clays containing innumerable pockets and