340 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



specimens showing a gradation from any one type to any other. ■ The 

 different kinds are, on the whole, fine and even grained aggregates of 

 white feldspars and dark, nearly black pyroxene, hornblendes, and biotite 

 flakes. The various components usually are distributed uniformly so that 

 on moderately fresh surfaces, the rocks present the appearance of being 

 composed of a finely granular, white ground peppered with tiny dark 

 grains and larger but still small, prismatic individuals of the dark coloured 

 constituents. In both the finer and coarser grained varieties, the relative 

 amounts of the dark and light coloured components vary from place to 

 place, and where the augite or hornblende is exceedingly abundant, the 

 rock assumes a very dark grayish, almost black colour, especially noticeable 

 in the case of the finer grained varieties. On the other hand, with increas- 

 ing proportions of feldspars, the general colour becomes a" lighter gray, a 

 colour more often shown by the coarser than the finer grained kinds. 



' Though the rocks are predominantly of a fine and even grained type, 

 yet it often happens that the dark pyroxene or hornblende occur partly in 

 larger prismatic individuals scattered through the finer, uniform material 

 of the bulk of the rock. Very small scales of dark mica are usually present 

 but as a rule in small proportions. Sometimes the minute, shining flakes 

 of this mineral become quite abundamt and in some instances larger, ragged 

 individuals with diameters up to one half of an inch are present and 

 enclose the other constituents as in a meshwork. 



' When thin sections of the monzonite are viewed under the micro- 

 scope, the pyroxene is seen to be a pale green augite often forming pris- 

 matic individuals seldom measuring more than an eighth of an inch in 

 length. The augite with secondary hornblende is always the chief, and 

 in some cases, virtually the only coloured constituent. At times it forms 

 a large proportion of the whole rock while in other cases, it is completely 

 overshadowed by the feldspars. Brown biotite is usually present in the 

 form of small scales or larger, irregular poikilitic flakes. The feldspars are 

 predominantly, sometimes altogether, of plagioclase varieties. The individ- 

 uals are generally lath-shaped and in many instances appear to be of the 

 composition of acid labradorite. An alkali feldspar is often present and 

 sometimes is quite abundant, either in ii-regular grains or in larger, plate- 

 like bodies enclosing the plagioclase laths. Some of the varieties of mon- 

 zonite contain much magnetite, others scarcely any, while small apatite 

 crystals are almost universal. 



' The monzonite is older than, and is cut by, the porphyritic monzonite, 

 the Nelson granodiorite, the pulaskite, and by a large series of dykes. It 

 apparently also is invaded by the diorite porphyrite. The monzonite body, 

 though having a sinuous outline, seldom seems to send offshoots of any 

 size into the older Carboniferous sediments and associated porphyrites 

 which so largely surround it. At three localities only, possible exceptions 

 to this general ride were observed. Within the augite porphyrite near the 

 southern boundarv of the area and just to the east of the westerly band of 



