XXXI V THE PALEONTOLOGY OF MINNESOTA. 



The ' ' Green and Blue shales and limestones " with a thickness of 60 to 100 feet, are 



next above the Galena. They are supposed to be in a general way, the equivalent of the 



Blue limestone of the Ohio geological reports and of the Utica slate, the Frankfort slate, 



the Pulaski shales and sandstone and the Lorraine shales of the New York geological 



reports. So far as noticed this is the first reference of the "Blue shales and limestone" 



of Ohio to this horizon in the Northwest, although they had been stated to be of the 



age of the Hudson Eiver group in 1842 by Prof. Hall. The Blue limestone of Ohio had 



hitherto been regarded, even by Hall, as suggested by Dr. Locke, as equivalent with the 



Trenton, and the term was transferred from Ohio to the Mississippi valley for that 



reason.* This series in New York had a thickness of 800 to 1,000 feet, but gradually 



diminishes westward. The characteristic organic remains are lamellibranchs, trilobites 



and bryozoans. The brachiopods are Strophomena, Ortbjs and Rhynchonella. Orthis 



occidentalis and Strophomena alternata occur in the upper beds in the southwestern part 



of the state and adjacent parts of Iowa. However, the most abundant and characteristic 



fossils of the upper beds in the southwestern part of the state are a small Nucula and a 



Clidophorus, along with a small Pleurotomaria and an Orthoceras. The fauna of these 



beds in the lead region is different from that of the same strata in the region of Green bay. 



J. D. Whitney. 



1862. Report upon the Lead Region, comprising chapters II, III, IV, V, and VI, of the 

 " Report on the Geological Survey of Wisconsin, vol. i. 1862, " last mentioned. 



The term "Blue limestone" here is made to cover all the strata from the top of the 

 St. Peter sandstone to the bottom of the Galena, comprising a vertical series of from 50 to 

 100 feet. The term "Buff limestone" is quite subordinate, being applied to a non- 

 important " buff -colored stratum" designated by that term by Dr. Owen in the map 

 accompanying his report of 1840, as revised and republished in 1844. This term, and the 

 stratum to which it was applied, came to be known as the Buff limestone in all later 

 reports. It has a thickness of about 25 feet, and is supposed to be the equivalent of the 

 Chazy, Birdseye and Black River limestones of New York. Its characteristic fossils are 

 large Orthocerata, Lituites undatus, Maclurea magna, Columnaria alveolata and several 

 species of Murchisonia and Pleurotomaria. 



The Blue limestone (supposed to be the New York Trenton limestone) is said to be a 

 pure limestone, with abundant remains of animal life. The first ten feet above the Buff lime- 

 stone, very compact, brittle, and breaking conchoidally, are known as the "glass rock, "but 

 in the eastern portion of the lead district this term is applied generally to any portion of the 

 Blue limestone. The thickness of the Blue averages perhaps 50 feet. 



The Galena is a crystalline dolomyte, 250 feet thick. 



" Toward the north this formation gradually dies out, and soon disappears after crossing the water- 

 shed. * * * * There are carbonaceous layers occasionally met with in the body of the Galena 

 limestone which are not only so impregnated with organic matter as to take flre and burn with flame 



* This reference of the Ohio Blue limestone to the Hudson Elver was later confirmed by the report of a committee of 

 the Cincinnati Society of Natural History, published In the Journal of the Society, pp. 193-194, January, 1879. See also the 

 tenth report of the Indiana Geological Survey, p. 23, 1879. 



