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WILLIAM HERBERT HO BBS 



compass dial. The order of importance of the series for the local 

 district is not quite the same as that for the larger district of which 

 it is a part, for beyond all question the east- west direction is the pre- 

 dominant one. Of the entire region, also, so far as it contains ores, 

 the mineralized crevices are mainly equatorial and meridional, less 

 frequently "quartering" (corresponding to a diagonal series). 



A glance at the map of Fig. i is sufficient to show that there 



Fig. 2. — Control of direction of a stream by prevailing joint planes in south- 

 western Wisconsin. (Photograph by Mr. E. C. Harder.) 



is more than an accidental coincidence of joints and drainage systems. 

 The map further reveals the distribution of. the observations, from 

 which distribution their relationship to near- lying drainage lines 

 may be made out. That the correspondences were not due to mere 

 coincidence is further attested by actual disclosures in the stream 

 valleys where the zigzags of the course follow actual joint planes 

 (see Fig. 2). 



The Richland Center district is included within the driftless area 

 of Wisconsin. Evidence of joint-controlled drainage is also furnished 

 by a district lying within the glaciated area of western New York. 



