SAINT LAWRENCE D(>L()>rlTKS AND SHALES. lio 



an unknown thickness, is irregularly stratified and consists of conglom- 

 eratic dolomite and quartz sand in its visible portion. It is consider- 

 ably colored with the same green mineral noticed in the two overlying 

 layers. A peculiar concretionary structure appears here which resem- 

 bles somewhat the Spirophyton cauda-galli of the Devonian, but is prob- 

 ably not of organic origin. 



We thus have, at the typical locality, 13 feet of dolomite exposed. 

 From N. H. Winchell's original descri2)tion * we learn that he considered 

 the rock silicious and harder than the Shakopee, evenly bedded and 

 specked with green. 



At Jordan, Minnesota, we find immediately beneath the Jordan sand- 

 stone a layer of dolomite six feet thick, soft, considerably altered by the 

 percolation of water, and almost rainl)ow-colored in places. It is con- 

 glomeratic at the top. l^elow lies another layer, fine and firm, which at 

 four feet from its top passes beneath the water level of the creek. The 

 lithologic characters of the layers are slightly different. For instance, 

 there is more coloring, locally, in the upper stratum and the second 

 one is finer textured and discloses no absorbed fossils, so far as ex- 

 plored. 



On the northwest quarter, section 12, Judson township, Minnesota, 

 the uppermost layers of the Saint Lawrence formation are seen. They 

 show varying lithologic and structural phases, as do the outcrops around 

 Jordan and Saint Lawrence, already noted. In section 2, Judson town- 

 ship, along a sloi)e descending from the crest of a terrace, blocks of dolo- 

 mite are scattered. From eight to twelve feet l)elow these blocks is a 

 small (piarry of thinly laminated dolomite, line sandstone and green 

 shale. Among tliem is one stratum of a more massive dolomite. Pass- 

 ing from this quarry northwestward many layers are concealed, while a 

 few are exposed. Among the ex[)osed and weathered slal)s along tlie 

 road are some of a semicrystalline, crinoidal character. The most west- 

 erly exposure of the magnesian series in the northwestern states is at 

 Judson post office. The rock at this place is the same ])ed that occurs 

 at Saint Lawrence. In traversing the distance from section 12 to the 

 post office one ])asses <lown 40 or 50 feet in vertical descent from tlie con- 

 tact of the Saint Lawrence and Jordan sandstone. 



THE REDWIXG SECTION. 



At lit'du'ing, .Minnesota, occurs one of tlie l)est localities tlius far found 

 in the nortliwest for the study of the Saint Lawrence formation. A l)ald, 



•Geol. ftnd Nat. His. Survey of .Minnesota, Second Ann. Rep., 1873, p. 162 tt atq. 



