REPORT OF THE CHIEF ASTRONOMER 603 



SESSIONAL PAPER No. 25a 



place in the range, along which the Kintla canyon, as a subsequent feature, 

 has been slowly developed. The unnamed lake just east of the monument on the 

 Great Divide, together with the outflowing creek, occupies a short valley 

 which seems to have a consequent course down the northeastern slope 

 of the minor anticline at the summit. On the other hand, Cameron Falls 

 Brook (Oil creek) in its lower part (below the sharp elbow) is clearly located 

 in the heart of a similar, narrow anticlinal roll and has the relation of a sub- 

 sequent stream. Subsequent streams, that is, those which are adjusted to soft 

 rock-belts, seem, however, to be very rare both in the Boundary belt and in the 

 finely mapped areas covered by the Kintla Lakes and Chief Mountain quad- 

 rangles of the United States Geological Survey. True obsequent drainage is 

 necessarily limited in the same proportion. 



The numerous lakes of the ranges are of Glacial or post-Glacial origin. 

 Lower Kintla lake has been formed by a dam of morainal material, though it 

 is possible that a true rock-basin also exists beneath its surface. Soundings 

 of over 300 feet are reported in this lake. Upper Kintla lake is partly or 

 altogether due to damming by a strong alluvial fan flung out across the canyon 

 from the south. Many other small lakes of the ranges are true rock-basins and, 

 as such, have been discussed briefly in the preceding chapter. 



For a brief account of the relation of topography and structure in the 

 Lewis range, the reader is referred to Willis's often quoted paper of 1902.* He 

 points out that, as in the Clarke range, the main syncline is accidented by 

 at least one narrow anticlinal fold. He has followed this fold from Mt. Cleve- 

 land southward to Mt. Gould. The former peak is the highest in the range 

 and Willis shows that the greater heights are coincident with the axis 

 of this arch, implying a ' general relation of mountain belt to anticlinal zone.' 



He writes further : ' In northern Lewis range and in Livingston [Clarke] 

 range greatest altitudes are in general related to anticlines.' It should be 

 observed, however, that the Mount Cleveland anticline and, as well, a 

 similarly narrow one at the summit monument in the Clarke range, are merely 

 local rolls in the floor of the master syncline, so that we may also hold that the 

 greater heights are related to a general synclinal axis. 



Like the present writer, Willis was unable to find many examples of possible 

 stream adjustment in either of the two ranges, and there seems to be no doubt 

 that most of the streams in the region have really consequent courses. This 

 conclusion is of moment in view of the fact that each range is composed of 

 rocks of very considerable differences in strength. Such heterogeneity would 

 almost certainly involve much more adjustment of the streams to soft belts 

 than we actually discern, if the region had ever been reduced to the condition 

 of a peneplain. Yet this is the definite view reached by Willis as a result of 

 his studies during 1901. Its discussion may well be postponed until" a short 

 description is given of the physiographic features of the Galton-MacDonald 

 mountain group, for Willis holds that that group was peneplained during the 

 same erosion cycle. 



* B. Willie. Bull. Geol. Soc. America. Vol. 13, p. 346. 



