HISTOKICAL SKETCH. 83 



1850, Owen.] 



The survey of Owen, so far as it threw light on the state ot Minnesota, 

 sei'ved for a reconnoissance, and indicated within certain broad limits the 

 general topography and geology. It first established the Lower Silurian 

 age ot the rocks outcropping along the upper Mississippi valley, and 

 especially of that forming the brink of the falls of St. Anthony which had 

 generally been regarded as Carboniferous. Under the general term " pro- 

 tozoic rocks," he describes the "lower sandstone of the upper Mississippi," 

 which he says may be seen in the lower portions ol the bluffs of the 

 river, and in the sandstones of the Minnesota valley above Shakopee. In 

 the upper portions of this great formation he brought to light an interest- 

 ing and very important series of organic remains, and in its lower portions 

 he found beds charged with Lingulce and Orbicuke. He enumerates six 

 horizons that hold trilobites, the uppermost separated from the lowest by an 

 interval of about 500 feet, though it is highly probable that some of these 

 trilobite beds are contemporary, and that the actual thickness of this forma- 

 tion is somewhat less than 500 feet, as developed on the upper Mississippi. 

 Nowhere in his report does Dr. Owen parallelize these beds with the Pots- 

 dam sandstone of New York, but seems to believe that the " palaeozoic base" 

 of the Mississippi as seen on the St. Croix river, is from seventy - five to one 

 hundred feet lower than the parallel of the " Lingula beds" of the New York 

 Potsdam, which, up to that time, had been regarded as the lowest fossil- 

 iferous base in the United States (page 50). But in the appendix (p. 634) are 

 tables of the equivalency of the geological formations, and of the strati- 

 graphical distribution of genera ot fossils, in which, presumably constructed 

 by Dr. Owen, this formation is parallelized with the Potsdam ot New York 

 state.* Under the term " protozoic rocks " he not only includes the lowest 

 sandstones but also the rest of the Lower and Upper Silurian. He separates 

 the limestones ot the Northwest into Lower and Upper Magnesian, the 

 former being that which" still retains that name, though by him and his 

 corps always confounded with the Shakopee limestone of Minnesota, in the 

 same manner as he confounds the outcrops of the Jordan sandstone with 

 the "lowest sandstone". In the latter he has included the Galena of the 

 Lower Silurian and the Niagara of the Upper Silurian, having failed to 



See also Proc. Accul. Nat. 3d. Phil. 1852. p. 190. 



