172 W. H. HOBBS — REPEATING PATTERNS IN STRUCTURE OP LAND 



joint system of the district, important deductions may be made relating 

 to the nature of the displacement on individual faults. Among the many 

 faults represented on the model, let us confine our attention for the mo- 

 ment to the most important — that which divides the main block longitu- 

 dinally on a medial line. The throw on this fault does not begin with a 

 small value, increase gradually to a maximum, and then die out grad- 

 ually; on the contrary, it is subject to the most abrupt changes, amount- 

 ing even to reversal of the thrown limb at points where the fault passes 

 from the end of one pair of blocks to the beginning of the next. Near 

 the center of the model the throw has been reduced to nothing, and on the 



Figure 42. — Floating Block Topography of the Orenaug Hills, near Woodbury, 



Connecticut 



(Hobbs, U. S. Geological Survey) 



traditional conception might be thought to have come to an end; but a 

 little farther on it quite as suddenly takes on values which approach the 

 maximum. Eeversals of the thrown limb are exhibited near the middle 

 of the section of the fault. It will be noted that the abrupt changes occur 

 where cross-faults intersect and where in consequence streams are likely 

 to be located. 



EVIDENCE FURNISHED BY EARTHQUAKES 



Until quite recently faults had been studied in the field only where in 

 part disclosed through denudation processes, and the opportunity to 



