Geology. — “On the Geological position of the Oil-fields of the 
Dutch East-Indies.” By Prof. G. A. F. MoOLENGRAAFF. 
(Communicated at the meeting of June 26, 1920). 
Experience has taught that the majority of the large oil-fields 
have originated in long enduring geosynclines, where these are 
marginal areas of sedimentation along the coasts of continents. *) 
In those geosynclinal belts, which are characterized by a long con- 
tinued subsidence of the soil, the organic matter in the sediments, i.e. 
the remains of animal and vegetable organisms may, as the subsidence 
of the soil proceeds, successively be covered by layers of fine sedi- 
ments. Thus, being shut off from water and air these organic remains 
may escape from destruction by oxydation. They may then be 
accumulated to a considerable thickness. As long as in such a geo- 
synclinal coastal belt, subsidence prevails over sedimentation, the 
area remains covered by the sea; if, however, sedimentation gets 
the better of subsidence, the area may become land. 
In the first case petroleum or allied hydrocarbons may be ulti- 
mately formed in the subsiding area; in the second case coal or 
allied substances may finally be found. A slow and gradual sub- 
sidence, the area meanwhile remaining all the time either low land 
‚or shallow sea, affords the most suitable conditions for the accumu- 
lation of such fossil fuels. Through the shifting of the equilibrium 
between the processes of subsidence of the soil and sedimentation, 
as well as through epirogenetic movements of land and sea relative 
to each other, every geosynclinal area may during its long life be land 
at one time and sea at another. Thus in the same geosyncline an 
accumulation of coal may take place at one time, and of petroleum 
at another; consequently in one and the same geosyncline coalbeds 
1) Among the recent publications bearing on this subject the following deserve 
special attention: M. R. Daty, Geosynclines and petroliferous deposits. Trans. 
Amer. Inst. of Min. Eng. LVII, p. 1054, 1918 and the discussion on it, ibid. 
p. 1065. W. F. Jones, The relation of oil-pools to ancient shorelines. Econ. Geol. 
XV, p. 81, 1920 and the discussion on it, ibid p. 350. 
