AREA COVERED BY BOUNDARY COMMISSION SURVEY 333 



of a belt crossing the Cascades between the Similkameen and Skagit 

 rivers and exactly bisected by the international line. To the officials at 

 Washington the writer is indebted for the use of this map in manu- 

 script. The belt averages 5 miles in width. The geology of the belt 

 has been plotted on the map, and the section has been continued eastward 

 by the use of a contour map of a similar 5-mile belt crossing the Interior 

 plateaus east of Similkameen river; in the latter map the international 

 line forms the southern limit. The total area of the belt which is of 

 present interest is about 400 square miles. The part lying within the 

 Hozomeen range — that is, west of Pasayten river — covers greatly de- 

 formed strata of Cretaceous age. The remainder, or three-fourths, of the 

 belt is underlaid by the vast assemblage of plutonic intrusive rocks which 

 had been briefly described by Smith and Calkins. 



This strip of rugged mountains forms part of a huge batholithic area 

 that will be adequately mapped only after many more seasons of arduous 

 field-work. The geological findings within such a belt as now to be de- 

 scribed would be much increased in value if they could be systematically 

 compared with field studies throughout the whole batholithic province. 

 For many reasons such a complete survey is now impracticable. The 

 present paper is thus a sort of report of progress on the geology of these 

 crystalline rocks of the northern Cascades. Nevertheless discoveries of 

 prime importance to the geology of the entire range have been made 

 within even the limited area of the 5-mile belt. Certain of the broader 

 conclusions there deduced may, it is believed, be relied on, and will not 

 need serious emendation as the exploration of the mountains continues. 

 In the following pages there is offered another class of considerations 

 which are theoretical and need the facts of the field, especially of the 

 whole Cascade field, for their full discussion. In these matters partic- 

 ularly, a 5-mile belt can not speak for the whole Okanagan range, except 

 as geological experience in that belt accords with verified geological ex- 

 perience the world over. 



General Description of the batholithic Area and Location and 

 relative Size of its Units 



From the eastern slope of the wide valley occupied by Osoyoos lake to 

 the Pasayten river, an air-line distance of just 60 miles along the boun- 

 dary, the mountains are composed of almost continuous plutonic igneous 

 rocks. This immense mass is markedly heterogeneous. To simplify the 

 following discussion it will be well to review the general geographical rela- 

 tions among the different geological units. To the same end it is con- 



