REPORT OF THE CHIEF ASTRONOMER . 429 



SESSIONAL PAPER No. 25a 



syenite families (see Figure 28). These crop out on the western summits of the 

 Kruger-mountain plateau and may be referred to as the Kruger alkaline body. 

 The Similkameen granite preserves what seem to be remnants of its once 

 complete roof (see Figure 31). Chopaka mountain is crowned with a large patch 

 of schist. This Chopaka schist is cut by a strong body of gabbro apparently 

 transitional into pure olivine rock — the Chopaka basic intrusives. The whole 

 forms a huge irregular block of roof rock surrounded by the Similkameen 

 granite. Excellent exposures show that the contact surface between the granite 

 and the schist-gabbro mass dips beneath the invaded formations (Figures 29 and 

 30). The writer has little doubt that the relations indicated in the figures are 

 typical of the whole boundary of the older terrane and that the granite underlies 

 the visible block in every part. In a similar section more than a half mile in 

 length the granite can be seen actually underlying the schist occurring on Snowy 

 mountain. 



ROOF-PENDANTS. 



Each of these schist-blocks, once a downwardly projecting part of a roof in 

 stock or batholith, may be named a ' roof-pendant ' or simply ' pendant.' It is 

 analogous to the pendant of Gothic architecture. 



A brief digression on this conception may be permitted. Unusually fine 

 examples of roof-pendants are illustrated in the great slabs of bedded rocks 

 interrupting the areas occupied by the batholiths of the Sierra Nevada. One of 

 the most recent descriptions is published by Messrs. Knopf and Thelen, follow- 

 ing the lead of Lawson in a study of Mineral King, California.* Other examples, 

 so well treated by Barrois, were found during the detailed geological survey of 

 Brittany. f In all these and many other cases, and yet more clearly than on 

 the Forty-ninth Parallel, the masses of country-rock (invaded formation) form 

 respectively parts of a once continuous roof. The often perfect preservation of 

 the regional strike in each of many examples very strongly suggests that these 

 slabs have not sunk independently in their respective magmas. Such partial 

 foundering would have almost inevitably caused some twisting of the block out 

 of its original orientation. Granite and block have come into present relations 

 because the magma, and not the block, was active. The point is of importance, 

 as it bears on the mechanism of intrusion in these instances. It is further 

 worthy of note that determination of roof -pendants and their distribution may 

 sometimes lead to the discovery of the approximate constructional form of 

 batholiths. 



A small pendant, composed of amphibolitic and micaceous schists and of 

 quartzite, occurs on the north slope of Horseshoe mountain; another of similar 

 constitution flanks the summit of Snowy mountain. 



In all three cases the pendants appear in the highest portions of the batho- 

 lith as now exposed in the belt; yet each block projects downward, deep into the 

 heart of the granite mass. 



•Bulletin, Department of Geology, University of California, Vol. 3, No. 15, 1904, 



and Vol. 4, No. 12, 1905. 



f C. Barrois : Annales, Societe Greologique dn Nord, many volumes, especially Vol. 22, 

 1894. p. 181 



