205 



IsTiAGARA Group Unconformities in Indiana. 

 Moses N. Elrod, M. D. 



Prof. Richard Owen, in the Indiana Geological Survey, 1859-60, calls 

 attention to an unconformity near Huntington, which he supposed to 

 indicate the dividing line between the Devonian and Upper Silurian. He 

 describes the arenaceous limestone of the Devonian as resting uncon- 

 formably, rate of dip 25 to 40 degrees southeast, on the silicious limestone 

 of the Silurian. Of the Linn's Mill exposure, on Treaty Creeli, Wabash 

 County, he says: "Here we again found evidence of the convulsions and 

 unconformable stratification noticed at the Fair Ground quarries of Hunt- 

 ington and in this county. On the west side of the creeli, opposite the 

 mill and close to the dam, a hill is formed by an anticlinal axis, the 

 beds dip northward and southward about 43 degrees. But the extreme 

 summit of the hill has evidently been subsequently denuded and abraded 

 by water until a hollow affords a channel for a rippling rivulet, while in 

 the bed of the main stream, beneath the axis, the undisturbed sti'ata are 

 visible." In the light of more recent investigations it is probable Prof. 

 Owen's arenaceous limestone of Huntington and the upper member of his 

 Wabash Coimty unconformities should be correlated with the porous lime- 

 rock of Prof. CoUett, and the picket rock of Messrs. Elrod and Benedict. 

 It suould also be noted that the underlying layers of stone, at Ti-eaty 

 Creek, are approximately horizontal, and exclude an uplift as the cause 

 of the distorted bedding. 



Prof. John Collett, in the Geological Survey of Indiana, 1872, describes 

 an unconformity seen by him at Calvert's quaiTy, near Geoi-getown, Cass 

 County. He found a gray limestone resting unconformably on the "silico 

 magnesia with a small parting of clay." This clay parting, he claims, is 

 general, and is often found in wells some 20 or 30 feet below the surface 

 at Logansport. At a later period the observations of Prof. Collett were 

 confirmed by Mr. A. C. Benetlict. Commenting on a section made, near 

 Georgetown, for the report on the Geology of Cass County, 1894, he de- 

 scribes the surface of the first layers under the "gray limestone" as show- 

 mg evidence, when exposed, "of having been eroded into channels and 

 hummocks before the overlying rock was deposited." 



Prof. Collett. under the section of his 1872 report devoted to Wabash 

 County, cdn^elates the '•gray limestone seen at Logansport and at a few 

 localities in Miami County" with the "thin-bedded paving stone" of Wa- 



