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and on the Isles of Nipigon Bay are numerous places where Keweenian strata are capped by thick sheets of trap, identical with those which cap the Animikie, but, though these sheets cannot be traced in absolute continuity in the interval, there are many outlying patches which fill the gap. The same trap sheets are found in several instances to pass from the Animikie to the Keweenian, and there are the same evidences of intrusion of independent trap sheets in the Keweenian that are in the Animikie. These rocks are, therefore, of post-Keweenian age, and, to discriminate them from the Keweenian and Animikie, they are designated the Logan sills.

Comments:—The fact that all the trap sheets of the Animikie studied by Lawson are intrusive is no evidence that in other areas, not studied by him, there may not be contemporaneous volcanics. The traps in the Triassic of Connecticut and New Jersey are an illustration of this point, a part of them being extrusive and a part intrusive. Also in the Penokee series, the equivalent to the Animikie series, while for the main part of the area there are no contemporaneous volcanics, in the eastern end of the series there suddenly appears a great thickness of contemporaneous volcanic fragmentals, and such may occur in the Animikie in the areas not yet studied.

The inclination of the Animikie series was fully recognized by Irving and Ingall, and this it was which led them to make their estimates of the thickness. The statement, that the strata have been dislocated by a great system of faults, may be true, but in the paper it is not supported by any evidence; and, until detailed evidence is presented, the conclusion of Irving and Ingall as to the thickness seems more probably true than the hypothesis of numerous faults.

Because the sills are later than the Animikie and Keweenawan strata which they have intruded, is no sufficient evidence that they are post-Keweenawan. The thickness of the Keweenaw series is so great that it is quite reasonable to expect that correlative with the later extrusions were intrusions between the older Keweenawan strata. To explain all the facts cited on the nortwest coast it is only necessary to suppose that the upper part of the Keweenawan has been removed by erosion, and that the sills now composing the upper layers in these places were overlain at one time by higher members, which have subsequently been removed by erosion. This is not a violent suppositition, for it is well known that erosion and volcanic extrusion alternated many times in single areas during Keweenawan time.