252 THE GEOLOGY OF THE MALAY PENINSULA. 
{ Fossiliferous blue clays and 
Kama clays | sandy beds. The main oil-bear- 
ing formation of Burma. 
ie es ‘ ee 
Pegu Upper Prome series {( Fossiliferous sandstones, clays, 
mA - 5 < v 
system \ Lower Prome series ( and shales. 
Unfossiliferous shales, resting 
Sitsavan shales ) unconformably on Eocene num- 
mulitic limestone. 
\ 
The outcrop of Kama clavs extends along the Irrawaddy Basin, 
and on it are situated the oil fields of Yenangvaung, Singu, Yenan- 
evat, Minbu, and ooee smaller fields. The Petroleum, being 
hehter than water. has been imprisoned along the axes of the antic- 
lines, wherever a laver of impermeable rock has formed a roof to 
prevent it from escaping, and bores are put down along the crests 
of the folds to tap it. Gases have also collected, and the mud 
volcanoes of the Arakan coast and at Minbu owe their origin to 
the escape of such gases alone fissures. 
The Kama clays are overlain by the Irrawaddy system of flu- 
viatile deposits, attamminge a thickness of 20,000 feet, which were 
once known as the “fossil-wood group” owing to the abundance of 
drift-wood contained in them. Emergence of the land took 
place im the north of our area sooner than in the south, and the 
retreat of the shore line from north to south began at the end of 
the Pegu period. In the north the Irrawaddy rocks are all fresh- 
water beds, whereas in the south, as‘in western Prome, the lower 
part of the Irrawaddy svstem includes some marine beds. Detailed 
work by oil geologists shows that in some districts there is consi- 
derable unconformity between the two series. 
In the plain of Irrawaddy beds, east of the Irrawaddy River 
and in the southwest of Yunnan, strong volcanic activity took place, 
building up the great volcanoes of Popa and Hawshuenshan. 
As already mentioned, these eruptions are many miles to the west 
of the boundary-fault between the Tertiary rocks of the Irrawaddy 
Plain and the older rocks of the Shan Plateau. Popa is fifty miles 
northeast of the Yenangyaung oil field. 
The basalt dyke at Loi Ling, in the Northern Shan States, 
is a Tertiary volcano, but here there was a much smaller display 
than in the Irrawaddy Plain and in Southwest Yunnan. 
The fresh-water Tertiary beds of the Northern Shan States 
are silts and soft sandy rocks with seams of brown lignitic coal, 
filling lake basins. These basins in the older rocks are the result of 
faults which occurred towards the close of the Tertiary period, 
and the lacustrine beds in them are either of late Tertiary or 
Pleistocene age. They have been found in six places, the most 
Jour. Straits Branch 
