THE INDEPENDENCE SHALE NEAR BRANDON, IOWA 



A. O. THOMAS 



On June 23, 1876, at the first annual meeting of the Iowa Acad- 

 emy of Science at Iowa City, Prof. Samuel Calvin read a paper 

 entitled "Preliminary Notice of Some Dark Shales near Indepen- 

 dence, Iowa." The paper was not published but early in 1877 an 

 abstract of it appeared in the American Naturalist, Vol. 11, pp. 57- 

 58. In this abstract the shale is referred to the Marcellus due to 

 its position below certain limestones, then believed to be Hamilton, 

 and due also to the presence of a shell presumably of Marcellus 

 age. The shale had been discovered in the bottom of a more or 

 less temporary quarry by Mr. D. S. Deering, one of Professor Cal- 

 vin's students. 



Calvin's more complete description^ of the shale and its unique 

 fauna appeared the next year. From this we infer that the shales 

 were stratified and undisturbed while "In some of the beds are 

 numerous remains of plants." Later, in the Buchanan county re- 

 port, Calvin states that in "shafts sunk at the Kilduft' quarry, 



. . the formation was penetrated to a depth of twenty feet and 

 was found to consist of dark-colored shales, alternating with beds 

 of limestone."^ On page 229 of the same report Calvin adds that 

 "It was in an abandoned pit a few rods west of the O'Toole (Kil- 

 duff) quarry, that the first shaft which brought to light the Inde- 

 pendence shales of this locality was put down." Thus it will be 

 seen that the earliest knowledge of this terrane and its fossils was 

 gathered from artificial exposures which in a few years were com- 

 pletely covered up. From these exposures and supported by evi- 

 dence acquired by a little digging, Calvin constructed a section of 

 the Devonian rocks of Buchanan county placing the Independence 

 shale below the Gyroceras beds.^ The failure of the shales with 

 their easily recognized fossils to appear in many places at this hori- 

 zon in other counties along the eastern border of the Iowa Devonian 

 belt has led workers — and correctly — to refer stratigraphically equi- 

 valent terranes, even though barren and lithologically different, to 



iBull. U. S. Geol. Geogr. Survey Terr., IV, pp. 725-730. 1878. 



=Iowa Geol. Survey, Vol. VIII, p. 222, 1898. 



'Amer. Geologist, Vol. VIII, pp. 142-145, 1891; also Vol. IX, p. 359, 1892. 



