17<5 TDE MAKQUETTE lK02f-BEAlllNG DISTKICT. 



ainthiuii' l)iit iiltcn-d igneous rocks. It is impossible to trace them back 

 to ail earlier source than a molten mag-nia; therefore, whatever may have 

 been the origin of this magma, we are justified in calling the rocks igneous. 

 There is no evidence of anv kind to support the belief that the gneissoid 

 granites in this portion of the ^lanjuette district were ever water-deposited 

 sediments that have been crystallized by metamorj^hic processes. 



THE HORNBLENDE-SYENITE. 

 DISTRIBUTION AND TOPOGRAPHY. 



The svenitc, with its gueissoid phases, so far as has been observed, is 

 found only in a narrow belt, from a quarter of a mile to a mile in width, 

 Iviiig between the green schists on the south and the fragmental beds of 

 the Silver Lake Algonkian area on the nortli. The belt is about 5 miles 

 long, and it lies almost entii*ely within T. 48 N., R. 26 W. (Atlas Sheets 

 XXX and XXXIII). The syenite is so like the granite in its nature that 

 but little remains to be said concerning it, except to describe its microscop- 

 ical features. The topography of the area occupied by it is exactly like 

 that of the granitic country. 



RELATIONS TO ADJACENT ROCKS. 



The relations of the syenite to the surrounding rocks are also like 

 those of the granite. Its apophyses cut the green schists, and its main 

 mass is unconformably beneath the Algonkian sediments. As to the rela- 

 tions existing between the syenite and the gi'anite nothing is yet known 

 positively. A very few ledges of the gneissoid granite have been found 

 within tlie limits of the syenite area, and these, when examined with refer- 

 ence to the latter rock, appeal- to have been intruded by it. The appear- 

 ances, however, are not decided enough to warrant an expression of opinion 

 as to their meaning. 



PETROGRAPHICAL CHARACTER. 



The primary constituents of the syenite are orthoclase, plagioclase, 

 hornblende, sphene, magnetite, and, ^•ery rarelv, biotite. Its secondary 

 components are plagioclase, microcline, chlorite, (juartz, epidote, muscovite, 

 and leucoxene. 



