of a divergent subordinate fold along the fracture Hue or axis of which 

 the escape of gases occurs. The general trend of this axis is nearly 

 east ami west in the region of the deposit, which is bounded (in the 

 north by the .Santa Monica Hills, and on the south by another gently 

 rising anticline. Jt dips so abruptly southward into the productive area 

 of oil just north of the brea beds, that at Jess than two miles to the 

 south of the field no well-paying oil sand has been found, even at a 

 depth Of 5320 feet. 



The various changes in elevation of the Pacific Coast have produced 

 changes in the conditions of erosion and deposition, resulting in an 

 environment more or l< ss favorable to the development of plant and 

 animal lift'. Evidences are abundant to show that at one time in the 

 history of the southwest this area was lower and more marshy; the 

 climate was milder, the rainfall more abundant, vegetation more luxuri- 

 ant, giving rise to a correspondingly highly developed fauna, and support 

 to a greater variety of forms. This semi-tropical condition was suc- 

 ceeded by a rise of the land, the fall of temperature, and the " 'ice 

 age" or glacial epoch was ushered in. The snow and ice extended far 

 to the south, especially in the higher altitudes, and gave the death 

 chill to the life of the pre-glacial or Pleistocene time. 



It was at this time, about two hundred thousand years ago, that 

 the plants and animals of Rancho La Brea perished and were buried. 

 The subsequent sinking of the land resulting in the change of rain- 

 fall and temperature, brought about the melting of the ice, and intro- 

 ducing the present age. The slighter subsequent changes of level, both 

 local and general, have caused many local disturbances, and it is sug- 

 gested that the breaking and scattering of the bones in the Brea 

 deposit have been due to such causes, but this is without evidence in 

 the beds themselves. In fact, the general miring of animals and the 

 scattering of their bones -by carnivores, and the drifting by water, 

 followed by the natural settling of the deposit in such accumulations, 

 are quite sufficient to account for all changes noted. 



The very remarkable number of vents through which the gas is 

 constantly escaping all over this area in and around the Brea deposits, 

 suggests * the probability of another line of fracture, composed of 

 numerous disconnected minor direct and reverse faults, extending south- 

 west from the subordinate flexure, and, just as the fault zone along 

 the line of the sudden dip, referred to above, marks the northern boun- 

 dary line of the richest productive area, so the abundant escape of gases 

 along the line of the Brea beds suggests another line of fracture which 

 may reach the southern limit of the productive field. Strength is given 

 to this idea by the logs of the wells in the area south of the beds, 

 which show oil seeps at various depths, but in no paying quantities. The 

 failure of the deepest well to find a profitable basin of oil sand indi- 

 cates broken strata filled with joint cracks, giving rise to slight displace- 

 ments and tiny fissures. If this surmise be substantiated, then there is 

 little hope of finding much oil south of the Brea deposit region. The 

 Tar Springs have formed no insignificant part in the role for the 

 accumulation of oil, tar and water throughout the whole mass of 

 material. Thus as the materials were forced upward by great pressure, 

 the gas carried the oil, tar and water with it. This mixture impreg- 

 nated the previous beds of formations, making local oil and tar lakes, 

 until finally in the upward course, reaching the top of the vent, tar 

 springs ami lakes naturally occurred on the surface. The bursting gas 

 bubbles left tar-lined cavities of varying dimensions, which soon became 

 filled with water, and the seeping oil saturated the ground, rendering 

 the subsoil quite soft and sticky. 



Ki 



