REPORT OF THE CHIEF ASTRONOMER 503 



SESSIONAL PAPER No. 25a 



' The upper part of the series comprises large volumes of volcanic 

 material, which it was not found practicable to separate, on the preliminary 

 map, from the slaty rocks. These old volcanics are for the most part extensively 

 developed on the southern end of Palmer Mountain, in the basin southeast 

 of that point, to the west of Blue Lake, and on the hill southwest of Palmer 

 Lake. Lithologically, they were roughly classified in the field as greenstones. 

 In broad, distant views the dark brownish hues of the weathered surfaces 

 and their rugged erosion forms give them a re-semblance to basaltic rocks. 

 In hand specimens their original character is found to be obscured by de- 

 composition, but the porphyritic texture is occasionally noted, as well as 

 amygdaloidal structure and brecciated structure suggestive of pvroclastic 

 origin. Microscopic study of these rocks is productive of no very satisfac- 

 tory results, owing to the advanced decomposition which they have univer- 

 sally suffered, the original materials being almost always completely re- 

 placed. The character of the resulting secondary minerals, however, as well 

 as the textural features, confirms the field diagnosis of the rocks. They are 

 basic extrusives, probably for the most part basaltic, though perhaps includ- 

 ing some basic andesite. Pyroelasties appear to be fully as abundant as the 

 massive lavas. 



' The rocks tentatively referred to the Cache Creek series have suffered 

 various degrees of metamorphism. The sedimentary portions have in 

 general an indurated slaty character in the localities removed from granitic 

 intrusions. In the vicinity of the several intrusive granite contacts, how- 

 ever, much more advanced alteration has taken place, the slates being more 

 or less completely converted to mica-schist. Interesting changes have been 

 produced also in the basic eruptives by the granitic intrusions, the description 

 of which will be deferred to the chapter on petrography. 



' The upper part of Jacks Mountain or Mount Nokomokeen, is carved 

 from a series which has the aspect of being much older than the Cretaceous 

 rocks farther east and may be equivalent to the supposed Cache Creek of 

 Okanagan Valley. It comprises both sedimentary and volcanic rocks. 



'Most prominent of the sedimentaries are quartzites and bedded cherts. 

 The latter are generally of a light-gray or drab tint and are cut by innumeiv 

 able veinlets of quartz. Their bedding is their most noteworthy feature. 

 They are built up of distinct laminae, about an inch in average thickness. 

 readily separable from one another. The similarity of their structure with 

 that of the red cherts of the Franciscan series in California is striking. As 

 in the supposed Carboniferous of Okanagan Valley, there are beds of lime- 

 stone (which are, however, rather thin and lenticular), and the 

 highest portions of the mountain reached was built up largely of altered vol- 

 canic rocks, among which amygdaloids were observed. Although obscured 

 greatly by alteration, the constitution and texture of these rocks as observed 

 under the microscope indicate that these old lavas are basaltic 



'Old schists, slates, cherts, and quartzites are also the' principal country 

 rocks in the valley of the Skagit above Ruby Creek, as far north as Jackass 



