C URRENT PRE- CAMBRIA N LI TERA TURE 1 9 1 



sandstone. The basaltic rocks forming the Bohemian Mountains pre- 

 sent phenomena which indicate their eruption subsequent to the for- 

 mation of the main deposits of the region, although the question is as 

 yet open. Subsequent to the deposition of the Keweenawan a fissure 

 was formed near the contact of the Eastern Sandstone and the lavas, 

 along which normal faulting occurred, the copper-bearing series form- 

 ing the overhanging side of the fault. As to the nature of the dis- 

 placement, however, more evidence is needed. The copper occurs in 

 fissure veins, in melaphyres, and in conglomerates. 



Comments. — That the Keweenawan was deposited on the Eastern 

 Sandstone was held by Wadsworth before the publication of Irving's J 

 report on the copper-bearing series in 1883. In his report Irving pre- 

 sented evidence to show that this could not be the case, but that the 

 sandstone is post Keweenawan ; and later, in 1885, Irving and Cham- 

 berlin 2 in a more comprehensive discussion of the relations of the 

 Keweenawan to the Eastern Sandstone, proved still more clearly the 

 post-Keweenawan age of the Eastern Sandstone. Subsequently, in 

 1893, Wadsworth took the view that the Keweenawan formed the 

 lower part of the Potsdam, and explained the phenomena on the 

 theory that the Eastern Sandstone, instead of being one sandstone, 

 may contain two or three sandstones of different ages. In the article 

 above reviewed Wadsworth has gone back to his earlier view. How- 

 ever, he has not yet met the arguments so clearly stated by Irving 

 and later and more comprehensively, by Irving and Chamberlin. 



Berkey 3 describes and maps the geology of the St. Croix dalles of 

 Wisconsin and Minnesota. Keweenawan eruptives are exposed at 

 numerous localities, and particularly along the river, where, by their 

 erosion, they have formed the dalles of the St. Croix River. The dip 

 is about 1 5 to the south, which would give a thickness to the rocks in 

 sight of 4000 feet. At several localities the Basal Sandstone uncon- 

 formable' overlies the Keweenawan eruptives with visible contacts, the 



'The copper-bearing rocks of Lake Superior, by R. D. Irving : Mon. U. S. Geol. 

 Surv., No. V, 1883. 



2 Observations on the junction between the Eastern Sandstone and the Keweenaw 

 series on Keweenaw Point, Lake Superior, by R. D. Irving and T. C. Chamberlin : 

 Bull. U S. Geol. Surv., No. XXIII, 1885. 



3 Geology of the St. Croix Dalles, by C.JP. Berkey: Am. Geol., Vol. XX, 1897, pp. 

 348-383, and Vol. XXI, 1898, pp. 139-155, 270-294. 



