CONTROLLED FRACTURE FIELDS OF NORTH AMERICA 



149 



have been found to run parallel to the northeast-southwest lines of the 

 drainage network^ and by utilizing the information derived from this 

 source concerning spacing, 

 Doctor Miller has been able 

 successfully to^ follow out the 

 continuations of interrupted 

 ore bodies. In both these ex- 

 amples it should be noted not 

 only that the drainage net- 

 work betrays a definite ori- 

 entation of waterways along 

 either the cardinal or their 

 bisecting directions, but that 

 there is a subequal spacing 

 of the streams in units of 

 different orders. Essentially 

 the same orientation and 

 spacing is betrayed by one 

 of Harder's published maps 

 from southwestern Wiscon- 

 sin.^^ Buckley has shown 

 that the prevailing joints in 

 practically all quarries of 

 Wisconsin indicate a domi- 

 nance of the four directions 

 toward the cardinal points 

 and along their 

 lines. He says:^^ 



Figure 24. — Drainage Map of the Area about 

 Rockland^ in northern Michigan 



Showing an arrangement of streams on north- 

 south, east-west, and northwest-southeast lines, 

 bisecting '^^^ divisions in the margin represent miles. (Nel- 

 " list's map) 



"As will be seen by the accompanying map, the joints of the sedimentary 

 rocks strike in four main directions. The prevailing general direction of the 

 joints is northeast and southwest. The other directions are northwest and 

 southeast, east and west, and north and south." 



On the north shore of Lake Superior the vertical dikes of Keweenawan 

 rock are in two series, one of wide dikes trending northeast to southwest, 

 the other of narrow dikes about northwest to southeast. ^^ Like directions 



M Harder : The Richland Center District. Loc. cit, pi. 3. 



'3 E. R. Buckley : On the building and ornamental stones of Wisconsin. Bulletin of 

 the Wisconsin Geological and Natural History Survey, No. 4, 1898, p. 459, pi. 49. 



8< A. C. Lawson : Twentieth Annual Report of the Geological and Natural Hlatorj 

 Survey of Minnesota, 1893, p. 198. 



