334 THE CAMBRIAN. [bull. 81. 



Another horizon is mentioned in which lies the Upper Calcareous 

 band, possibly marking the horizon of the Mendota limestone of cen- 

 tral Wisconsin. 



At no one point in tlio district is the entire formation exposed, and so, to obtain 

 the entire thickness from the Lower Ma^nesian limestone to the granite below, the 

 sum of tho thicknesses of the subdivisions is taken : 



Feet. 



From the Lower Magnesian to the Hudson trilobite bed 200 



From the Hudson trilobite bed to the Eau Claire Trilobite bed . 200 



From the Eau Claire Trilobite bed to the Eau Claire grit 240 



From the Eau Claire grit to the granite (at Eau Claire), esti- 

 mated 100 



Total 740 



Tho last division is probably much thicker to the south and west, making the 

 thickness of the formation range to 800 and 1,000 feet. 1 



The report of Prof. Wooster contains details of numerous local sec- 

 tions that show the lithologic and paleontologic characters of the forma- 

 tion. 



The outcrops in Iowa are the continuation of those of southwestern 

 Wisconsin ; and very little is added to the knowledge of the formation 

 in Minnesota, where it is called the St. Croix sandstone by Prof. N. H. 

 W 7 inchell. At Winona and Stockton there are about 303 feet of the 

 formation exposed. 2 



A generalized section in Minnesota, as given by Prof. Winchell, 3 is 

 as follows: 



Feet. 



( Jordan sandstone 75-100 = Madison of Wisconsin. 



St. Croix < St. Lawrence limestone 0- 30 = Mendotaof Wisconsin. 



( Dresbach sandstone and shales 200. 



Shales (?) 



CANADIAN EXTENSION. 



In the account of a deep boring at Rosenfeld Station, on the Canadian 

 Pacific Railway, Dr. G. M. Dawson correlates the upper portion of the 

 section with the Maquoketa shales, beneath which occurs the Galena 

 limestone, passing below into Trenton and then to the St. Peters sand- 

 stone. Below this, before reaching the granite, there are 110 feet of 

 dark red, reddish and greenish, bluish and grayish shales, passing be- 

 low into red shales, which are referred with doubt to the Lower Magne. 

 sian limestone. 4 Whether the St. Croix sandstone is represented in 

 this section can not be determined in the absence of paleontologic evi- 

 dence, but it is not improbable that the horizon of the St. Croix and the 

 Lower Maguesian limestone of the Minnesota section may both be in- 

 cluded between the limestone aud the granite at the bottom of the well. 



>Op. cit.,p. 112. 

 2 Tho Geology of Minnesota, vol. 1 of the final report. 1884, p. 258. 



3 Winchell, N. H.: 14th Ann. Rep. Minn. Geol. and Nat. Hist. Survey, 1886, pp. 325-337. 



4 On certain borings in Manitoba and the Northwest Territory . Royal Soc. Canada, Proc. and Trans. , 

 vol. 4, section 4, 1887, p. 86. 



