130 REVIEWS 



results arrived at by geotectonal, through petrographic, considerations, 

 in the attempt to retrace the geological history of the West Indies. 



A paper received December 27, from Dr. Callaway presents in the 

 description of the structure of the island of Anglesey a remarkable 

 parallel with that of the island of Cuba.' 



Some Results of the Late Minnesota Geological Survey. By N. H. 



WiNCHELL. 



This paper mentioned some of the scientific conclusions and some 

 of the known economic results reached by the survey, presented in the 

 final report. Among the scientific conclusions have been: the defini- 

 tion of the parts of the Upper Cambrian in the upper Mississippi 

 valley ; the identification of the Potsdam sandstone as seen at Pots- 

 dam, N. Y., with a quartzitic sandstone which was found to be a part 

 of the Keweenawan ; the definition of the Lower Silurian and its 

 parts ; the determination of the eastern extent of the Cretaceous ; the 

 discovery and announcement of the duality of the ice-epochs ; the 

 determination of the length of time elapsed since the last (or Wis- 

 consin) ice-epoch, through the recession of the falls of St. Anthony ; 

 the formation of glacial lakes about the ice-border; the origin of 

 kames (now called eskers) in ice-walled gorges ; the superglacial 

 position of the drift while being transported, especially in proximity 

 to the ice-margin ; the duality of the iron-bearing formations in the 

 Lake Superior region, and the later discovery of a third horizon ; the 

 separation of the Archean en masse into two non-conformable parts, 

 viz., the upper and the lower Keewatin, with a great basal conglom- 

 erate between them ; the detection of the oldest known rock in the 

 Lake Superior region (the greenstones called Kawishiwin), the sup- 

 posed earliest crust of the globe; the origin of the Mesabi ores in a 

 greensand which has been altered, affording iron oxide by concentra- 

 tion ; the contemporary deposition of oceanic silica from solution ; the 

 original greensand, and pebbles and breccia associated with it, as well 

 as sheets of basic lava of the same date, were of volcanic origin ; the 

 well-known jaspilytes of both Mesabi and Vermilion ranges were 

 originally the result of silification of volcanic obsidian (supplementary 

 to the hypothesis of Wadsworth), but sometimes were broken and dis- 

 tributed so as to constitute secondary jaspilyte beds ; the formation of 



^ " Plutonic complex of Central Anglesey," Quarterly Journal of the Geological 

 Society, Vol. LVIII (November, 1902). 



