Geology and Natural History. 497 



2. The Geological and Natural History Survey of Minnesota 

 for the year 1887. 504 pp. 8vo, with plates and other illustra- 

 tions, N. H. Winchell, State Geologist : containing two reports 

 on the Original Huronian rocks, and others referred to the Hu- 

 ronian, including the Animike group, the iron-bearing series, and 

 underlying crystalline rocks, one by Prof. N. H. Winchell, and 

 the other by Prof. A. Winchell; and also a report on the crys- 

 talline rocks by H. V. Winchell. 



Field Studies in the Archaean Rocks of Minnesota with 

 accessory observations in Ontario, Michigan and Wisconsin, by 

 Alexander Winchell. 504 pp. 8vo, Ann Arbor, 1889. 



The second of these volumes consists of the reports of Prof. A. 

 Winchell for the years 1886 and 1887 to the Minnesota reports of 

 those years. The investigation of the " Original Huronian " by 

 Professors N. H. aud A. Winchell has led them to similar conclu- 

 sions. The results are here cited from the report of the latter. 

 The section made conforms in most points with the descriptions 

 by Logan in 1863, and on his map of 1865. The succession of 

 rocks commencing with the oldest, and excluding, as igneous, the 

 chlorite rocks and greenstones, is stated to be as follows : 



1. Missisagui quartzyte, 3750 feet thick; 2, Bruce limestone 

 100 ft; 3, Lower slates or argillyte, conglomeritic and sili- 

 ceous, 7400 ft; 4, Red felsyte, granulyte and quartzyte, 100 

 ft; 5, Upper Slates or argillyte; 6. Otter-tail cherty limestone, 

 100 ft; 7, Thessalon quartzyte, red and gray, 5000 ft; 8, Otter- 

 tail quartzyte, white, 4000 ft. None of the rocks are crystalline, 

 except locally at a contact with an eruptive. The White quartzyte, 

 the uppermost stratum, occupies the north shore as far as St. 

 Mary's River and along part of St. Joseph's island. Here it is 

 overlaid directly by a siliceous fossiliferous limestone, apparently 

 the Chazy, and hence it is probably Lower Cambrian. 



From a study of the Marquette iron region, the conclusion is de- 

 duced that the rocks underlie the true Huronian, and are uncon- 

 formable to it, while " not separated from the Laurentian by a 

 structural unconformability." The Animike formation, on the 

 north shore of Lake Superior, which stretches from Thunder Bay 

 nearly to Duluth, and is recognized still farther west, is essentially 

 argillitic, with siliceous layers, and with some iron-ore (magnetitic 

 beds) in the upper part, and is generally nearly horizontal in bed- 

 ding. It is made the equivalent of the " slate conglomerate " of the 

 typical Huronian. The Kewatin series of argillitic, sericitic, chlo- 

 ride and micaceous schists, high in dip, occurring about Vermil- 

 lion Lake and elsewhere (and including the so-called Vermillion 

 series), is an independent system older than and unconformable to 

 the Animike. The Ogishke conglomerate of the vicinity of 

 Ogishke-Muncie Lake, with the associated slates, is perhaps of the 

 Animike series, but probably underlies it. 



Many important facts are detailed and illustrated in the reports 

 with regard to the relations of granite to the schists, and to brec- 

 cia granite, and conglomerate granite, and also to gradual transi- 



