186 THE CAMBRIAN. [bull.h. 



Mr. Warren Uphara in notes on the geology of Minnehaha County, 

 Dakota, 1 refers to the rocks in various portions of Minn ehaha County 

 as " Typical Potsdam quartzite," but he mentions no reasons for conclud- 

 ing it to be of this a.ge. No fossils were found in it. 



In the second volume of the Geology of Minnesota Prof. N. H. Win- 

 chell states that the St. Croix formation in Wabasha County is about 

 250 or 300 feet in thickness ; and it is not known to vary particularly 

 in its stra tigraphic composition from that of Winona Co unty. 2 In the 

 account of the geology of Goodhue County he describes the formation 

 and accompanies it with a list of the fossils found in the St. Croix 

 formation in the Upper Mississippi Valley. 3 



In the same volume Mr. Warren Upham describes the St. Croix sand- 

 stone as it occurs in Chisago County,in the valley of the St. Croix Kiver. 4 

 He also describes the formation as it occurs in Pine County, along the 

 upper portion of the St. Croix Kiver. 5 



In an article on the age of the St. Croix sandstone, Prof. N. H. 

 Winchell discusses its relations to the typical Potsdam of New York 

 and concludes it is a distinct formation. 6 In an account of a deep well 

 drilled at Stillwater, Minnesota, it is stated by Mr. A. D. Meads that — 



The well starts at about 740 feet above the sea, and after passing through 701 feet 

 of drift, white friable sandstone, and green shales belonging to the St. Croix and so- 

 called Potsdam of the Northwest, enters a series of dark red and brown shales and 

 brown feldspathic sandstones which exhibited a thickness of more than 1,500 feet. 

 These gradually assume characters of a volcanic detrital tuff — " amygdaloidal," cal- 

 citic, kaolinic, still brown, slightly siliceous — and finally at the depth of about 3,300 

 feet unmistakable beds of trap rock were encountered, alternating with sandstone 

 beds. At this depth some grains of native copper were seen in the drillings. 7 



Prof. N. H. Winchell has recently published his latest conclusions on 

 the Taconic rocks of Minnesota. On the evidence of the tracks de- 

 scribed by Mr. G. F. Matthew 8 he considers the Taconic (Lower Cam- 

 brian) age of the " Animike" formation to be sufficiently established, 

 and thinks the name Taconic should be substituted for Animike. 9 The 

 Pewabic quartzite is referred to the base of the "Animike," although he 

 says: " it was at first supposed to be the equivalent of the Potsdam 

 (Paradoxides horizon) which apparently overlies the "Animike." 10 



A correction is made in relation to the reference of the stratigraphic 

 position of the Granular quartz as follows: 11 



I Notes on the geology of Minnehaha County, Dakota. Geol. and Nat. Hist. Survey, Minnesota, 13th 

 Ann. Rep. for 1884, 1885, pp. 88-97. 



2 The Geolog.y of Minnesota. Vol. 2 of Final Report, 1888, p. 13, 



'Op. cit., pp. 31-36. 



4 The Geology of Minnesota. Vol. 2, Final Report, 1888, pp. 407, 409. 



6 Op. cit., pp. 637-642. 



6 Geol. and Nat. Hist. Surv. of Minn., 17th Ann. Rep. for 1888, 1889, pp. 56-64. 



i The Stillwater Deep Well. American Geologist, vol. 3, 1889, p. 342. 



« Am. Jour. Sci., 3d ser., vol. 39, 1890, p. 145. 



9 The iron ores of Minnesota. Geol. and Nat. Hist. Suiv. Minnesota. Bull. No. 6, 1891, p. 113. 



10 Op. cit., p. 125. 



II Op. cit. Foot note on pp. 417, 418. 





