442 
vania and those of Argentina, may be mentioned: in the Pennsylvanian 
geosyncline, which has originated as a belt marginal to the then 
North-American continent (the archaean Canadian shield built out 
southward), the sedimentation, as well as the folding of the Appal- 
achians (Appellachia), which separated the inner portion of the geo- 
syneline from the Ocean to the south-east, reached its maximum of 
intensity in Pennsylvanian time, and closed in Permian time; the 
oil-fields in the Andine portion of Argentina are marginal to the 
ancient South-American continent, which, in geological structure, 
exhibits striking similarity to South-Africa and the so-called Gon- 
dwana-land. The sedimentation in that geosyncline occurred in 
Jurassic and in Cretaceous time, while the folding which was attended 
by intense volcanic activity and gave rise to the Andes, terminated 
in Tertiary time. As a third instance the oil-fields of Venezuela may 
be quoted. As soon as one considers this mode of development of 
an oil-field to be the typical one, such a field must show the following 
features (see fig. 1): 
1. a geosynclinal coastal belt G (fig. 1), being the depository of 
the sediments in which the hydrocarbons originate. The position of 
this belt will indicate in a rough way the original shore-line of 
2. the continental area ZL, from which the terrigenous material 
is derived, which gradually has been accumulated in the marginal 
geosyncline. This area may also be called the ancient continental 
area or the primary area of denudation, because it existed already 
as a landmass before the geosyncline had originated. 
3. the sea or ocean S, which, reckoning from the continent, lies 
on the other side of the geosyncline. 
In the geosynclinal belt one can distinguish : 
a. The portion near the land G, consisting of sediments deposited 
in a shallow sea or on a low land. These deposits consist preponderantly 
of terrigenous materials (limestones are rare) and contain coal-, or 
oil-beds or both. They are folded generally not very strongly during 
the last period of the orogenetic phase, which terminated a long era 
in the still longer life of the geosyncline. 
6. The portion G, more remote from the land in which the 
sediments, for a great part marls and limestones, were deposited 
farther away from the shore of the continent than in the portion 
G,. Generally this portion has been folded in a period of the oro- 
genetic phase prior to the folding of the portion G,. In that case 
the anticlinal parts of the folds had already emerged from the sea 
as rows of islands or more or less continuous strips of land or may 
be as lofty folded mountain-chains, whilst in G, the subsidence 
