148 W. H. HOBBS REPEATING PATTERNS IN STRUCTURE OF LAND 



pendicular northwesterly series, even if subordinate, is none the less 

 present ; as, for example, in the Duvani-Bnlla line to the northeast on the 

 map. 



THE ME8R-LIKE ARRANGEMENT OF VOLCANIC VENTS 



The arrangement of volcanic cones is generally ordered in a pattern of 

 lines which is often known to be, and at other times is believed to repre- 

 sent, fissure lines within the crust. This was long ago pointed out by 

 Darwin, and has found confirmation in the writings of many later vul- 

 canologists, notably Thoroddsen and Yerbeek. The meshlike arrange- 

 ment of volcanoes, and its origin in a fracture system, has on the basis of 

 recent literature been more fully discussed by the writer in another 

 place.^* 



The Correlation of Fracture Fields 



controlled fracture fields of north america 



WinchelFs "diagonal system" of Michigan had reference to the topo- 

 graphical and hydrographical features of the State of Michigan and 

 neighboring areas in Ohio, Wisconsin, and Ontario. Here the drainage 

 lines are very generally ordered in northeast-southwest and northwest- 

 southeast directions, as well as on the somewhat less important meridional 

 and trans-meridional directions. In this respect, then, the province may 

 be looked upon as having common elements of structure, whatever differ- 

 ences of rock composition or of geological history may be represented by 

 its component and widely separated parts. Such sections of the earth's 

 surface, which are chosen more or less arbitrarily on grounds of con- 

 venience, may be referred to as fracture fields. 



Any one who will take the trouble to examine the later maps of the 

 country surrounding the upper Laurentian lakes may easily convince 

 himself that the directions claimed by Winchell to control have exercised 

 a dominating influence on the hydrography. In figure 24 is reproduced 

 an area taken almost at random from the most recent hydrographic 

 map of northern Michigan, and in figure 25 the drainage network near 

 Lake Temiscaming, in Ontario. ^^ Within this district the cobalt veins 



80 Proceedings of the American Philosophical Society, vol. 48, 1909, pp. 17-26. 



31 W. G. Miller : The cobalt-nickel arsenides and silver deposits of Temiskamlng. Re- 

 port of the Bureau of Mines, vol. 14, pt. ii, 1905, pp. 28-31 ; ibid. (3d ed.), vol. 16, pt. II. 

 pp. 36-38, fig. 15. 



W. H. Hobbs : Transactions of the Wisconsin Academy of Science, vol. 15, pp. 15-29 

 (Issued August, 1905). 



L. V. Pirsson : Crustal warping in the Temagami-Temiskamlng district, Ontario. 

 American Journal of Science, vol. 30, 1910, pp. 25-32. 



