XXV111 THE PALEONTOLOGY OF MINNESOTA. 



"1. The Mound strata, consisting of three distinct beds of limestone; the upper, middle and lower. 

 2. A bed of Blue shale, separating the Mound strata from the next lower limestone series. 3. The 

 Upper Magnesian of Owen, also consisting of three distinct beds. 4. The Blue limestone, including the 

 Blue and Buff limestones of Owe.n (1st Rep.,) also presenting three distinct beds. 5. The Upper Sand- 

 stone. 6. The Lower Magnesian of Owen. ****?. The Lower Sandstone." 



The Blue shale here individualized, being the "Nucula bed" of Daniels, became sub- 

 sequently known as the Maquoketa shale. Percival calls attention to the small fossils, 

 but seems to have no idea, as yet, of the equivalence of this bed with the Hudson River of 

 New York. He gives it a distinct place in the lead region, viz., between the Mound 

 limestone (the Coralline limestone of Owen) and the Upper Magnesian limestone. The 

 term "Blue limestone" is here made to include the Blue and the Buff of Owen. 



J. G. Percival. 



1856. Annual report of the Geological Survey of the state of Wisconsin. By J. G. PER- 

 CIVAL; Madison, 1856; pp. 1-111. 



This is a continuation of the descriptions of Dr. Percival's first report. He gives more 

 details of the lithology of the several formations, spoken of in the other report, and the 

 characteristics of the minor divisions of each. He mentions shells of the genus Leptcena as 

 being characterastic of the "Blue limestone." Below the coralline beds of Dr. Owen he de- 

 scribes a blue shale "underlying the mound limestone, and thus immediately above the 

 upper magnesian," (p. 14). This he describes at numerous points in the Mississippi valley, 

 and affirms that it occurs in the eastern part of the state, describing it at several points on 

 the narrow peninsula which forms the eastern side of Green bay. This seems to have been 

 the first published identification of this shale with the Hudson River rocks of the east 

 shore of Green bay. 



James Hall. 



1858. Report of the Geological Survey of the state of Iowa, embracing the results of 

 investigations piade during portions of the years 1855-56, and 57. By JAMES HALL and J. 

 D. WHITNEY. Vol. I, parts 1 and 2 (in two volumes), 1858. 



In giving a general review of the formations (Chapter in) Prof. Hall states that the 

 "Trenton limestone with the subordinate beds of the Birdseye and Black River limestones, 

 preserve, at several points above Dubuque, upon Turkey river and other places in Iowa, 

 at Platteville and Mineral Point in Wisconsin, at the falls of St. Anthony and at St. Paul 

 in Minnesota, in a greater or less degree, their distinctness of character and position." 

 In a section at Pike's hill opposite the mouth of the Wisconsin river he includes the Trenton 

 and Birdseye limestones between the Galena and the "magnesian beds below," giving 

 them a total thickness of 75 feet. In other words, he excludes both Trenton and Birdseye 

 from that stratum of the Lower Silurian which later became known as the Buff limestone, 

 and which still later came to be considered exclusively as the Trenton. With these he also 

 must necessarily have excluded the Black River limestone. In a section at Clayton (p. 56) 

 he describes the Galena as alternating with the Trenton. The total thickness, between the 

 St. Peter sandstone and the Galena, he found at Guttenburg to be about 100 feet, and in 



