1852.) 189 
November 2d, 1852. 
Vice-President Bripces 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 Commissionersof 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 Qth. 
Vice-President BripGs&s 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, Xe. 
Dr. Owen, in presenting to the Academy. of Natural Sciences of Philadelphia 
a copy of the Geological Map of Wisconsin, lowa 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 Lae 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 dolomitie 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 exposures 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 PHILADELPHIA.—VOL. VI, NO. VI. yn, 30 .! 4 
