SCIENTIFIC BACKGROUND 121 



measurable movements have taken place in recent time. 

 The Carnegie people at Pasadena are preparing a series 

 of experiments to determine if such movements exist 

 or are detectable. 



TIME OF THE MOVEMENTS 

 Movements have been occurring along these fault 

 lines during long periods of time, in some instances 

 extending back to the close of the Eocene epoch of 

 Tertiary time. Try to conceive how long it has taken 

 to raise the great San Bernardino escarpment some 

 7,000 feet by little jog-like movements here and there, 

 along its extent. It defies the grasp of the human 

 mind, and yet this escarpment was made only yes- 

 terday in geologic time. The movements which have 

 produced the superb physiography of Southern Cali- 

 fornia have mostly taken place in prehistoric (Pleis- 

 tocene) time, but there are still occasional after-eifects 

 which cause the mild tremors of the present. Some 

 modern geologists, unfamiliar with the local geological 

 history, infer that the present-day movement is as act- 

 ive as in times past, but in my opinion this is a mis- 

 taken hypothesis. 



CROSS FAULTING 

 Definite knowledge exists in some instances that 

 faults of one directional group have cut across those 

 of another. Some of the master highlands are of a 

 complex structure and their outlines have been 

 blocked out by two or more fault lines of different 

 ages and directions. This has resulted in the fault 

 block or "paving stone" types of structure." 



The writer has previously shown that this crossing 

 of the structure trends of one age by those of another 



