48 N0ETL1NG : PETROLEUM IN BURMA. 



everything required for the existence of mud volcanoes, yet there 

 is not the slightest trace of them at either locality. From this it 

 seems quite clear that some other conditions must prevail which 

 cause mud volcanoes, and that clay, gas and water are not by them- 

 selves sufficient to produce them. 



The examination of the country around suggested, however, 

 an idea which may afford some sort of an explanation. I have 

 pointed out that the mud volcanoes are situated in an elon- 

 gated horseshoe shaped valley, filled with recent argillaceous beds. 

 It is probable that this horseshoe shaped valley has been caused 

 through subsidence of part of the miocene strata below ; at 

 least the appearance of the northern, eastern and western side seem 

 to support such a view, though it is possible that it is only a valley 

 of erosion. The question of the nature of this valley is, however, 

 only of secondary importance; the fact remains that here is a basin of 

 tertiary strata covered by recent alluvial beds. I believe the petro- 

 leum and gas rose along fissures in the tertiary beds below, and 

 were arrested by the impermeable layer of alluvial clay which covers 

 the tertiary beds as stated, so that when the pressure of gas and 

 petroleum collected immediately under this covering layer, had 

 acquired sufficient force to break through the superimposed alluvium, 

 it formed a mud volcano. In the other cases the pressure may have 

 been gradually relieved through existing fissures. As it is more than 

 probable that the alluvial clay rests on strata charged fully by ground 

 water, the above hypothesis would explain— 



(a) The low temperature of the mud ejected by the mud vol- 

 canoes. 



(5) Their periodical change of the activity. 

 The following diagram woodcut, fig. i, will illustrate this view, 

 but I must mention that I do not insist on this explanation being 

 applicable to mud volcanoes elsewhere. 



Unfortunately I have not seen yet the large mud volcanoes of 

 Ramri and Cheduba island on the Arrakan coast, and I cannot there- 

 fore say in what relation they stand to the mud holes of Minbu. 



I 94 ) 



