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are not uncommon, and hornblendic and pyroxenic gneiss appears in some places. The Fundamental Gneiss, so far as at present known, is a complicated series of rocks, for the most part of unknown origin, but comprising a considerable amount of intrusive material.

In certain parts of the Laurentian area, and notably in the Grenville district, the Laurentian has a different character. In the Grenville series the orthoclase-gneiss is still the predominating rock, although it here has a greater variety of mineralogical condition, and is frequently well foliated. Amphibolites, hornblende-schists, heavy beds of quartzite, and numerous thick bands of crystalline limestones, are all abundant and interstratified with one another. In the series are ores, and a wide variety of minerals. In the limestone and associated rocks graphite is often widely disseminated. This does not occur in the Fundamental Gneiss. The areas occupied by the Grenville series while together aggregating many thousands of square miles, are probably small as compared with those of the Fundamental Gneiss. The Grenville rocks, while generally highly inclined, over some large area are nearly horizontal, but even in these cases they have been subjected to great pressure.

As to the origin and relations of the Fundamental Gneiss and the Grenville series, three views may be taken:

1. The Fundamental Gneiss may be the remains of a primitive crust penetrated by great masses of igneous rocks and having been subjected to repeated dynamic movements. The Grenville series may be an upward continuation of the Fundamental Gneiss under altered conditions, marking a transition from a primitive crust to normal sediments. Thus the two would form one practically continuous series. The general petrological similarity of the two series, taken in connection with the more varied nature of the Grenville series, its frequent stratified character, and the presence in it of limestones and graphite indicating an approach to modern conditions and the advent of life, together with the difficulty of clearly separating the two series from each other and defining their respective limits, lend support to this view.
2. The Grenville series may be considered as distinct from the Fundamental Gneiss, and reposing on it unconformably, being a highly altered series of clastic origin, the Fundamental Gneiss having some such origin as suggested above or being an older series of still more highly altered sediments. As it is now thoroughly crystalline, there is, however, no absolutely conclusive proof that even the Grenville series is of sedimentary origin. However, the series is in all probability made up, in part at least, and perhaps wholly, of sedimentary material, but as this is not absolutely shown, the proposal to separate it from the rest of the Laurentian and class it as Algonkian or Huronian seems premature.