30 L. V. Pirsson — Crustal Warping in the 



upon. Bell,* in noting the course of Lake Temiskaming, sug- 

 gests that it follows the course of a great dike wliich has been 

 eroded ; a suggestion which J3arlow's geological map shows to 

 be untenable. Ilobbs,f in a short paper on fracture systems, 

 briefly alludes to this drainage plan and gives a map of a part 

 of the area showing its peculiar natnre. He attributes it to 

 joints. Miller;}: gives a more extended discussion of the systems 

 of lines, and states that it is impossible to tell whether they fol- 

 low faults or folds. 



A study of Barlow's geologic maps of the Nipissing and 

 Temiskaming sheets shows that these depressional lines of 

 drainage are independent of the distribution of the rocks. The 

 Montreal River, which holds a straight course tlu'ough gray- 

 wacke, slate, quartzite, and diabase, is a striking example of 

 this. In a few cases, however, as plotted on tlie map, they 

 appear to lie over the contact of formations. A consideration 

 of the strike, especially of the planes of foliation of the gneissic 

 areas, shows that they sometimes follow it, but just as often, 

 and especially in the larger depressions, cut directly across it. 



Either the drainage plan is directly conditioned by the present 

 rock structures, or it is one that has been inherited ; that is to 

 say, it is superimposed upon the present surface by overlying 

 formations, which once existed but have now disappeared. It 

 is true that a remnant of an overlying formation, generally 

 attributed to the JMiagara, is foi^nd at the north end of Lake 

 Temiskaming, but to restore this over the whole region would 

 not only involve great improbabilities but would in itself give 

 no explanation, for we should still have to account for the con- 

 ditions in such an overlying series which would initiate such a 

 drainage. It is also difficult to see how simple folding could 

 produce such a rectangular net- work. On the whole, as sug- 

 gested by Hobbs and Miller, it seems most probable that a sys- 

 tem of nearly right-angled jointing and faulting has initiated 

 planes of structural weakness through the region, which the 

 streams have taken advantage of, and which has thei'efore exer- 

 cised a directive control over them. While, as Miller remarks, 

 it is difficult to directly prove this, since such lines of weakness 

 in rock structure, or of displacement, are now for the most part 

 covered by lakes, streams, and swamps, yet some corroborative 

 evidence may be gleaned from Barlow's report vfhere the 

 jointed character of the rocks along the Montreal River is men- 

 tioned, and in one place of the direction of these joints as deter- 

 mining the course of the river.§ Many more such instances 

 should be found when the region is more closely studied. 



*Bun. Geol. Soc. America, vol. v, p. 365, 1894. 



t Trans. Wise. Acad. Sci., vol. xv, p. 19, 1905. 



X Eep. of the Bureau of Mines, Ontario, vol. xvi, ])i. ii, 1907, p. 36. 



§Loc. cit., p. 234. 



A 



