FILLMOKE COUKTY. 303 



Devonian limestones.] 



The Dernnian limestones. Since the report of the Iowa geological survey 

 of 1870, by Prof. C. A. White, in which the rocks of the Devonian were all 

 regarded as belonging to the Hamilton epoch, various new facts have been 

 brought to light in the Northwest, bearing on the age of the different parts 

 of the Devonian. Prof. S. Calvin has reported the existence of a dark shale 

 at least twenty-five feet in thickness, lying beneath the Devonian lime- 

 stones at Independence,* which he considers sufficiently similar 'to the 

 shales at Rockford, which overlie the Devonian limestones, to indicate that 

 all the Devonian strata of Iowa belong to a single group. Mr. W. H. Barris 

 has shown a fossil fauna in strata at Davenport that has a strong general 

 affinity with the Corniferous. | These same strata had in 1858 been assigned 

 to the Corniferous by Prof. James Hall. Some shaly beds at Rockford 

 Profs. Hall and Whitfield have also referred to the Chemung in the Twenty- 

 third report of the New York state cabinet. 



So far as the Devonian appears in Minnesota it may be grouped in three 

 parts, but to what particular portions of the New York nomenclature these 

 may belong, it is still impossible to state. 1. Shales and fine-grained, hard, 

 thin-bedded magnesian limestones. 2. Harsh magnesia?}, heavy-bedded limestones. 

 3. Fine, argillaceous sandstones, becoming arenaceous in some layers and calcare- 

 ous in others. Of these only the second is known in Fillmore county, although 

 it is possible that the first also exists beneath the drift in the elevated 

 portions of Beaver and Bloomfield townships. 



The Devonian limestones that appear in Fillmore county are very dif- 

 ferent, lithologically, from those that are found at Le Roy, in Mower county, 

 They have the outward aspect of the Corniferous as seen in the states of 

 Michigan and Ohio, and may be the equivalent of those strata, but owing 

 to the meagerness of outcrops in the county no comparison can be made ot 

 their fossils with those of the Corniferous of New York. 



The distinctively Onondaga features of the Ohio Corniferous | are the 

 only ones seen in Fillmore county. The color of the limestone is like that 

 of the Galena. Its texture is generally even and non-vesicular, harsh to 

 the feel and granular like most magnesian limestones. The bedding is 



'Bulletin of the United States Geological and Geographical Survey of the Territories. Hayden. Vol. IV., p. 725 

 tProcecdings of the Duvenport Academy of Sciences Vol. II., p. 261. 



tThat portion of the Ohio Carniferous here referred to is the lower as seen at Columbus, Delhi, and Millpoint. 

 The overlying blue beds, seen at Delaware, Marion and Sandu<ky,:are supposed to represent the Hamilton. See Proceed 

 m. Asto. Adv. Set.. 1873, p. 100; alto Am. Jour. Sci. and Arts, Apr., 1874. 



