112 IOWA ACADEMY OF SCIENCE 



With the recognition of this fault-line a host of features relat- 

 ing to the distribution of the formations of the region, hitherto 

 puzzling or uncertain of determination, are fully explained. 



North of Fort Dodge there are evidences of another fault 

 which passes through Pocahontas and which has a throw of 

 about eighty feet. The horizontal distance between the two 

 lines of displacement is approximately twenty-five miles. This 

 figure suggests the spacing value of the whole system. Plot- 

 ting upon the map of the state other lines to mark possible 

 positions of other faults we find abundant indications of the 

 presence of such features. One of these passing a short distance 

 south of Ames points to the isolated protrusion of Early Car- 

 bonic limestones being really produced by differential move- 

 ment along a line of rupture. 



It is a well known fact established through extensive ex- 

 perience in mining operations that when the interval between 

 two parallel faults is determined that other faults are to be 

 expected at like intervals. This circumstance is traceable di- 

 rectly to the nature of the tortional strains which rock-masses 

 undergo. Whether or not such a high spacing value as twenty- 

 five miles is actually possible remains to be determined theore- 

 tically. The problem is readily susceptible of mathematical dem- 

 onstration as in the cases of fault systems of much closer pat- 

 terns as recently noted by G. F. Becker 6 ; and it would be ex- 

 ceedingly instructive to apply the principles involved to the 

 Iowa situation. 



In any case the general geological mapping of the state re- 

 quires fundamental rectification. 



6 Bull. Geol. Soc. America, Vol. IV, 1893, p. 13. 



