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reinforced in the latter case by his map of Northwestern Minnesota, which suggests that the upper division of the Keweenawan overlaps the lower unconconformably.

In the first of these areas the thin-bedded flows are described as being poured out against the gabbro mass, which, it is said, must have stood to a great height, until finally the flows accumulated sufficiently to cap the upper surface of the gabbro. So strongly was Irving impressed by these facts, that he states that he was inclined at first to place the gabbros of the Bad River district with the Huronian, and to regard them as the equivalents of the great flows of the Animikie series of Thunder Bay, but, finding the Animikie slates unconformably under the gabbros, he preferred to put them as the earliest division of the Keweenawan, clearly recognizing that there was a very considerable unconformity between these coarse, massive rocks and the later thinly-bedded ones. This reference was made because of the close lithological relationship of the gabbro and the Keweenawan diabases, and because in eruptive series such breaks were regarded as less significant.

It thus appears that Irving fully appreciated an unconformity, probably at the horizon of Lawson's unconformity, but he did not recognize that the break which has so extensive an occurrence also exists along the Minnesota coast. If the explanation suggested as to the relations on the Minnesota coast be true, Irving's statements, used in reference to the Bad River area, can be applied almost exactly to this one, in which case the difference between Irving and Lawson is that of nomenclature. Lawson restricts the term Keweenawan to the upper part of the series, whereas Irving and other writers regarded the Keweenawan as including both divisions. It also follows, if the anorthosite is Keweenawan, that Lawson's conclusion that the Animikie is absent below the Keweenawan in Northeastern Minnesota, is without foundation, for the base of the Keweenawan thus defined is not here exposed. Further, the Animikie is certainly unconformably below the great basal gabbro of Minnesota. It further follows that the correlation of the anorthosites of Lake Superior and those of the Province of Quebec has no value. But, wholly apart from the stratigraphy of Northeastern Minnesota, I must confess to a complete lack of confidence in the correlation of eruptive rocks so far removed as these.

To the statement that Irving's subdivision of the Keweenawan into groups and his estimate of the thicknesses of various portions of the series are of little value, I feel that I must take exception. The painstaking character of all of Irving's work is well-known. He spent many years of study upon the series in Michigan and Wisconsin. His study, and that of his assistants, Messrs. Chauvenet, Cambell and McKinley, on the northwest coast of Lake Superior was of a detailed character. It would seem scarcely possible that Dr. Lawson's study of the stratigraphy in a single trip, in which he made no attempt to re-measure the sections (so far, at least, as can be ascertained from his paper) could have been detailed enough to warrant this sweeping state-