1852.] 189 



November 2d, 1852. 

 Vice-President Bridges in the Chair. 



Letters were read 



From the Asiatic Society of Bengal, dated July 9th, 1852, acknow- 

 ledging the receipt of the Journal of the Academy, vol. 2, part 2, and 

 of the Proceedings vol, 6, part 1. 



From the Chief Commissioners of H. M. Works and Public Buildings, 

 dated London, Sept. 15, 1852, acknowledging the receipt of copies of the 

 ^' Notice of the Academy by Dr. Ruschenberger,'' which have been de- 

 posited in the Museum of Practical Geology. 



From M. Haidinger, dated Vienna, 20th April, 1852, transmitting 

 the volumes acknowledged this evening. 



From the Academy of Sciences of Vienna, dated October 3d, 1852, 

 transmitting its works announced this evening. 



November 9th. 



Vice President Bridges in the Chair. 



A letter was read from the Librarian of the British Museum, dated 

 London, 21st Oct., 1852, acknowledging the receipt of recent Nos. of the 

 Academy's Proceedings, &c. 



Dr. Owen, in presenting to the Academy of Natural Sciences of Philadelphia 

 a copy of the Geological Map of Wisconsin, Iowa and Minnesota, just published, 

 made the following remarks : 



The region of country embraced in this geological map extends from latitude 

 38 to 49, and from longitude 89 30' to 96 30^ It has a length, from north 

 to south, of 750 miles, and its greatest width 270 miles, the area being 200,000 

 square miles. Embracing the Mississippi river and all its tributaries, from its 

 source to its junction with the Missouri ; the Missouri river, as high as Council 

 Bluff; the Red river of the north, from its source to the northern boundary of 

 the United States ; together with the northern and southern shores of Lake 

 Superior, from Fond du Lac north to the British dominions, and east to the 

 Michigan line. 



All the calcareous rocks are represented on this map by tints of blue; the 

 pure calcareous rocks being of pure blue tints, while the magnesio-calcareous 

 or dolomitic rocks are of shades of purple blue; the sandstones, of yellow; the 

 coal measures, of sepia; the metamorphic schists, of purple; the metamor- 

 phosed rocks, of Silurian date, of orange ; while all the igneous rocks are of 

 bright red colors. 



A very large tract of the northern regions of this district, being more than 

 one half of the country, is overspread with extensive drift deposites, penetrated 

 only at a few limited and distant points, (these chiefly in the deep cuts of the 

 streams,) by igneous rocks and metamorphic schists; except along the height 

 of land dividing the waters of Lake Superior and the Mississippi ; on the north 

 west shore of Lake Superior and the region bordering on the British dominions, 

 where the exposure of granite, gneiss, and metamorphic schists and trappose 

 rocks, are rather more extensive. 



The drift consists of deposites of sand, gravel clays of great thickness, of 

 marls, and, locally, of erratic blocks. The summit levels of this region are 

 from 500 to 1100 feet and more above Lake Superior. 



PROCEED. ACAD. NAT. SCI. OF PmLADSLPHIA. VOL. VI. NO. VI. 30 



