226 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



All three specimens are very fresh and their densities clearly indicate the 

 acidification along the upper contact. The respective specific gravities are: — 



No. 3, 15 feet below tipper contact 2-983 



No. 2, 425 " " " " 3-001 



No. 1, 480 " " " " 3-072 



Lower contact, 500 feet below upper contaot. 



MOYIE SILLS. 



Of all the intrusions those outcropping on the isolated ' M oyie Mountain/ 

 immediately west of the Moyie river at the Boundary line, show the most 

 remarkable variations in composition. (Figures 13 and 14; Plate 25.) 

 Some years ago the writer published two papers detailing the petro- 

 graphy of the more important phases of these sills.* The description 

 was based on field work during only a few days in the season 

 of 1904. The importance of this particular section was not fully appar- 

 ent until the field season was over and the rock collection had been micro- 

 scopically studied. If time could have been spared during the continued recon- 

 naissance of the Boundary belt, the writer would have early made a second 

 visit to the Moyie sills to test the conclusions of the 1904 season regarding field 

 relations. Unfortunately, no such opportunity for additional personal field 

 work became available. In 1905 an untrained assistant was sent to the locality, 

 and he collected new petrographic material at points along the Boundary slash, 

 as designated by the writer. The character of the specimens thus added to 

 the material in hand seemed to corroborate the general conclusions of the 

 writer and the two publications above mentioned were issued. 



Thus, in 1905 and 1906, the writer believed that the intrusive 'rocks occur- 

 ring on the western slope of Moyie mountain together form a single sill about 

 2,600 feet in thickness. Such was his belief at the time when the present 

 report was sent in for publication. In 1910, Mr. Stuart J. Schofield was 

 commissioned by the Director of the Dominion Geological Survey to make 

 a geological study of the Purcell range. At the writer's request, Mr. Schofield 

 examined the section of Moyie mountain at the Boundary slash. He found 

 that the igneous rocks of the western slope really compose three sills, separated 

 by Kitchener quartzite. He also found two thinner sills on the eastern slope 

 of the mountain and in the same Boundary-line section, an area which the 

 writer was not able to traverse in 1904. In 1911 Mr. Schofield guided the writer 

 to his various contacts, all of which were seen to be correctly located in his 

 profile of the mountain. Recent forest fires had cleared the exposures somewhat 

 since 1904 and there can now be little doubt as to the structural relations here- 

 after described. The writer's sincere thanks are due to Mr. Schofield for his 

 careful, efficient field-work on this problem. 



The relations are, therefore, more complex than was formerly believed by 

 the writer. However, it may be stated well in advance that the theoretical con- 



* American Journal of Science, Vol. 20, 1905, p. 185; Festscbrift zum siebzigsten 

 Geburtstage von Harry Rosenbuscb, Stuttgart, 1906, p. 203. 



