Loz^'cr Silurian of Wisconsin and Minnesota. 321 



nesota are the equivalents of the Upper Buff and Blue beds in 

 Wisconsin, with the exception of the first ten feet of our shales. 

 These last are, doubtless, a part of the Lower Blue bed in Wis- 

 consin. 



I came to the conclusion, some time ago, that the first strata 

 of the shales could be classed with the limestone below, as easily 

 as with the shales above. They form here a transitional bed, 

 which for convenience I wish to distinguish as the StictoporeUa 

 bed. The limestone strata, which constitutes part of it, though 

 crystalline like the slabs in the true shales above, are the result 

 of sedimentation like the limestones below. The fauna, too, is 

 as much that of the preceding as of the succeeding strata. 



The StictoporeUa bed, in ascending order, is as follows : 

 Limestone 6 in., limestone i ft. i in., limestone 2 ft., shale i ft. 

 6 in., limestone 7 in., shale 5 ft., limestone i ft. 6 in. (measure- 

 ments taken at Saint Paul.) 



The shaly parts are not unmixed clay, but have numerous 

 thin hard calcareous laminae in them. The stone and shale vary 

 locally in thickness and alternation, but are of about the same 

 proportion, as seen in Goodhue, Olmsted and Fillmore counties, 

 Minnesota. 



There is a bed of dark colored limestone upon the Lower 

 Blue bed at Platteville, Wis., which appears to be the same as the 

 StictoporeUa bed in Minnesota. It consists of, first, about four 

 feet of solid strata, with thinner cleavable strata of the same col- 

 or; second, three to four feet of green shale such as commonly 

 occurs in Minnesota; and third, four feet of dark colored stone, 

 apparently the transitional back to the ordinary limestone. The 

 fossils were most of them characteristic forms of the StictoporeUa 

 bed in Minnesota. 



At Dodgeville, Wis., the same strata, so far as I could judge, 

 occur as a light brown bed about ten feet thick, but quite unfos- 

 siliferous. At the time this place was examined, I was very much 

 puzzled as to whether this bed belonged to the Lower Blue or 

 Upper Buff limestone, but upon reading over the Geology of Wis- 

 consin, Vol. I, I became quite satisfied that it would be classified 

 as equivalent to part of the Lower Blue limestone of the Rock 

 river valley. 



Along the Illinois Central railroad near Dodgeville, nearly 

 every stratum from the Saint Peter to the middle of the Galena 

 is clearly exposed. There can be recognized the Lower Buff", 



