PETROLEUM POSSIBILITIES OE ELORIDA 
49 
Fig. 3. Diagram showing the conditions found near Fellows in the Midway- 
Sunset Field of California. After Pack. The dark bands represent oil sands. Near 
the surface and also separating the oil from the water are accumulations of tar as 
indicated in the sketch. 
FOLDED. STRATA 
Instead of being merely tilted, the rock strata may be folded in such 
a way as to form a trap to retain oil. A simple illustration would be a 
fold in otherwise horizontal strata such as is indicated by the accompany¬ 
ing sketch. (Fig. 4.) In this sketch the strata are bent up in such a way 
as to form a storage reservoir in the rock for oil and gas. In such a res¬ 
ervoir the gas is likely to be found near the axis, the oil next below the 
gas, and the water, if present, farther down the sides of the fold. 
A simple symmetrical fold such as is represented in this sketch is 
rarely found in nature. More commonly the folding is more or less 
complicated. 
anticlinal folds 
A fold such as is represented in Figure 4 is known as an anticline, a 
term applied to folds that arch upwards. As a rule, in nature an upfold 
is more or less compensated by a corresponding downfold. To the 
downfold there is applied the term syncline. Of the different strata of 
the formations as shown in this illustration, one is represented as a por¬ 
ous horizon into which oil and gas enter from below or above and mi¬ 
grate up the dip. However, upon reaching the anticline both the gas 
