172 HALL AND SARDESON — THE MAGNESIAN SERIES. 



A correlation of the Shakopee (Shakopee A) with the upper Calciferous 

 of New York and the Oneota (Shakopee B) Avith the lower Calciferous 

 seems to encounter few objections, although there is no present intention 

 to set forth a decided opinion. 



Thus it will be seen that the Magnesian series as understood by the 

 authors includes all of the Upper Cambrian in the northwest and a part 

 of the Lower Silurian (Ordovician), provided the Shakopee (Shakopee A) 

 be correlated with the upper Calciferous and both referred to the Lower 

 Silurian.* 



The Saint Lawrence Dolomites and Shales. 



localities. 



In Minnesota many exposures occur between Redwing and Lake City ; 

 at Rollingstone creek ; the railway cut above Stockton ; at Winona, Dres- 

 bach, Hokah, Stillwater, section 28 Saint Lawrence township ; Jordan, 

 section 30 Blakely township, and at Judson. 



In Iowa they are to be found at several quarries around Lansing. 



In Wisconsin they occur at Spring Green, Lone Rock, Lodi, McBride's 

 point lake Mendota, Hudson and vicinity, Trempealeau, La Crosse and 

 Osceola. 



At Saint Lawrence, Minnesota, is found the type exposure, the rock 

 in view representing the lower half of the formation. The Mendota lime- 

 stone at the type locality described by Irving f represents the upper 

 portion of the same formation. AVere a division advisable into two 

 parts the names Saint Lawrence and Mendota would not be synonyms, 

 but would stand for different beds in what is now considered a single 

 formation. 



SPECIAL FEATURES. 



At section 28 Saint Lawrence, Scott county, Minnesota, about one 

 mile south of Saint Lawrence landing, on the Minnesota river, there is 

 exposed in one of the quarries six feet of a buff colored dolomite. Irreg- 

 ular laminae of green shaly material are scattered through the entire 

 rock exposed. A few rods farther southwest and in another quarry one 

 foot of this soft greenish and laminated dolomite rock is seen overlying 

 harder strata of a more crystalline dolomite. This last carries numerous 

 green specks of varying sizes, which are commonly called glauconite. 

 For a thickness of four feet this rock is very evenly bedded and carries the 

 casts of a few absorbed fossils, particularly Orthis pepina, Hall. Beneath 

 this layer is still another, which is seen three feet and which reaches to 



* Compare Charles D. Walcott: Am. Jour. Sci., 3d ser., vol. xxxv, 1888, pp. 398, 399. 

 t Geology of Wisconsin, vol. ii, 1877, p. 534. 



