PAPERS ON GEOLOGY " 



THRUST FAULTS 



Many of the transverse folds are accompanied by thrust 

 faults. Some faults occur in the middle of an anticline and oth- 

 ers at the edge next a syncline. Some faults grade into folds 

 above, others feather out in the loose upper shales, while still 

 others break clear across the strata. Though the displacement 

 of beds is generally less than ten feet, and may be less than a 

 foot, many of the fault planes are marked by distinct brecci- 

 ated zones. The evidence of overthrust in one of these faults 

 seems very decisive, for the upturned edges of the soft shales 

 are still attached to the ends of the downthrown beds, while 

 the downturned ends on the upthrow side have been broken off 

 and ground fine by the movement of the upthrown rocks over 

 them (Fig 3). 



AGE OF FOLDS AND FAULTS 



The rocks themselves fix the age of the folds and faults only 

 as later than Devonian or Mississippian, but the relations of 

 these movements to glaciated surfaces, glacial deposits, ter- 

 races, and flood-plains, show that many of them are not only 

 post-glacial, but that they are later than the low stream ter- 

 races, and that a few of them are even later than the present 

 flood-plains. 



The evidence of recency is seen in the rise of the loose top 

 of a fold distinctly above glaciated surfaces on either side 

 (Fig. 2), and in the deformation of glacial deposits above the 

 fold in such a manner that surface drainage has been affected 

 and a recent gully started along the fold parallel to the axis. 



Other evidences of recency are found in the deformation 

 of the surface of a terrace by a fold or fault, and in the une- 

 roded condition of the top of fold or fault in a terrace (Fig. 

 4). 



In like manner, the deformation of the surface of a flood- 

 plain by a fold or fault, or the uneroded top of fold or fault 

 in the flood-plain, shows that it is more recent than the flood- 

 plain. 



Though not so definite as to time, other evidences of re- 

 cency are seen in the freshness of the brecciated fault zones 

 and in the unweathered condition of joints near the surface. 



CONCLUSIONS 



A reconnaisance was made by the writer of parts of the 

 larger streams flowing into Lake Erie from Sandusky, Ohio, 



