FILLMORE COUNTY. 289 



Trenton limestone.] 



The Southern Minnesota railroad here enters on its descent to the Root 

 river valley. 



The species of Lingulepis mentioned is found in No. 4 of the foregoing 

 section. The remains are exceedingly fragile, and as the grains of sand in 

 which they are embraced are feebly cemented together, it is nearly impos- 

 sible to transport or even to handle them without their falling to pieces. 

 These fragments, for no entire specimens were obtained, are arranged pro- 

 miscuously in the coarse sand, and are all confined within three feet of the 

 top of No. 4. They seem to have suffered the attrition and fracture inci- 

 dent to coarse sedimentary transportation. 



The remarks that have already been made on the topography of the 

 county, and the diagrams that have been given, will sufficiently elucidate 

 the nature of the St. Peter sandstone, and its important part in the causes 

 that have diversified the surface of Fillmore county. 



The Trenton limestone. That which has been described hitherto, in this 

 volume, as the Trenton limestone, embraces a thickness of strata amount- 

 ing to not more than twenty -five feet. These calcareous strata are over- 

 lain in Houston and Winona counties, by a series of shales and shaly strata, 

 embracing some lenticular layers of very fossiliferous limestone, likewise 

 belonging to the Trenton period, amounting to perhaps twenty-five feet, 

 which have been referred to the Hudson River epoch ot that period. In 

 Fillmore county, above these shaly strata, appears a considerable thickness 

 of other calcareous strata belonging to the same period, which are the 

 equivalent of the Galena limestone, and of the strata which in the reports 

 of progress were distinguished as Upper Trenton, amounting to about 125 

 feet. The exact position of these strata in the Trenton period it is not 

 possible to state, but there is some reason to include them all within the 

 Hudson River epoch, with some evidence of the presence also of the hori- 

 zon of the Utica slate.* 



It has already been stated that the "green shales" of the annual reports 

 seem to belong to the Hudson River group of New York. This is based 

 mainly on the lithological resemblance; yet the Trenton fossil Columnaria 

 alveolata, Goldfuss, was taken from these shales near St. Charles, in Winona 

 county. If this coral be regarded as diagnostic of the Trenton epoch, the 



Compare Transactions of the Albany Institute, Vol. X. June, 1879. The Vtica Slate and Bflaled Formations C. D. 

 Walcott. 



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