Preliminary report on the Marquette iron-bearing district of Michigan

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 Excerpt: ...the broad Ishpeming and Negaunee synclinorinm. The continued westerly pitch of the series brings the quartzite of the Upper Marquette to the surface at Ishpeming, and this divides the Negaunee formation into two arms, one of which extends along the south side of the Marquette area and the other along the north side. Therefore, west of Ishpeming, the formation appears in two belts on opposite sides of the great synclinorinm. At Lake Michigamme an intermediate anticline becomes prominent, and as a result of it a synclinal arm extending southeast, but terminating at Republic, is produced. West of the Republic fold is another very similar one. In the large Ishpeming-Negaunee area the secondary folding of the formation, combined with the distortions of the intrusions, produces an extremely complicated contact line, both with the underlying Siamo slate and the overlying Ishpeming quartzite. By studying these lines it is seen that the formation is rolled in a number of east-west folds, which produces several large reentrants and salients, each of which is composed of smaller reentrants and salients. The eastern swings of the contact lines mark synclines, and the western swings anticlines. Putting it in another way, the iron formation first appears above the Siamo slate in several fingers, each being a syncline. These to the west unite to form the broad area. Farther to the west the Ishpeming qnartzite appears and hides the iron formation in a manner exactly similar. The secondary folds are still further modified and complicated by the intrusion of igneous masses, about which the iron formation sometimes has a quaquaversal dip. (PI. XIX.) At other places the dip is but little modified by the intrusives. The western arms of the iron formation also have minor overfol...