278 INDEX TO THE STRATIGKAPHY OF NORTH AMERICA. 



concretions of lime phosphate. The nodules vary greatly in size, shape, and relative abundance. 

 Some are spherical and from a half to several inches in diameter; others are flattened or irregular 

 ellipsoids, sometimes as much as 2 feet in length and over 6 inches thick; and they may be 

 loosely disposed in the shale, or closely packed. The green color is due to the presence of 

 glauconite or greensand, a silicate of iron and potash. Rarely, as in the upper part of East 

 Fork of South Harpeth Creek, the green shale is absent or not distinguishable, and in these 

 cases the black shale seems to pass very gradually into overlying green shale, which constitutes 

 the base of the full TuUahoma section. 



Fossils are almost if not entirely restricted to the lower member of the Chattanooga forma- 

 tion. In the dark-gray variety of phosphatic rock, which is really a conglomerate, casts of 

 minute coiled and bivalve moUuscan shells, washed out of the Ordovician rocks forming the 

 surface of the land that was being gradually submerged, are very abundant. Waterwom bones 

 of large fishes not infrequently occur with them. In the basal shale and fine-grained sandstone 

 a species of Lingula, probably L. spatulata, is frequently seen, while the shiny teeth, jaws, 

 and cephalic plates of conodonts, supposed to be small fishes related to myxinoids, are often 

 found, sometimes in great numbers. 



In the table of correlations of the Columbia folio *^^^ the Chattanooga shale of 

 western Tennessee is placed as the equivalent of the Portage and Chemung of New 

 York. 



J 15-16. MISSOURI AND ILLINOIS. 



A narrow belt of thin Devonian strata extends from southern Illinois north- 

 westward into Missouri as far as Jefferson City. Keyes *^^ distinguished the Grand 

 Tower limestone, 100 feet, and the Callaway limestone, 70 feet thick, the latter 

 overlain by Kinderhook (Carboniferous) strata. The Grand Tower he referred to 

 the Oriskany and Onondaga epochs, and the Calloway to the Hamilton epoch. 

 The Onondaga fauna was also recognized by Weller *^^ near Grand Tower, 111. 

 Buckley,^"^ in a recent paper, describes the Devonian of southeastern Missouri as 

 composed of Clear Creek limestone (Oriskany age), at the base, overlain by Grand 

 Tower limestone (Hamilton and Onondaga age), with the Sulphur Springs forma- 

 tion, composed of several members, at the top. Weller *^^ and Ulrich " regard the 

 Sulphur Springs formation as being of Mississippian age and a part of the Kinderhook. 



The relations of the Devonian strata of northeastern Missouri to those of Iowa, 

 the significance of the unconformity between the Silurian and Carboniferous in 

 central Missouri, and the correlation of the Devonian of southern sections are con- 

 sidered by Keyes ^"^ in a general paper. 



The Devonian of Illinois has been discussed by WeUer *'^' **^ and Savage. ''"^^ 



Weller's article in 1897 is a detailed study of the zones which may be recognized 

 in the "Bake Oven" section, near Grand Tower, on Mississippi River. He distin- 

 guished seven conspicuous divisions comprising 26 faunal zones, from each of which 

 he gives a list of fossils. He concludes : ^""^ 



It is believed that the facts here set forth satisfactorily demonstrate that the Devonian 

 faunas in southern Illinois are not related to the lowan Devonian faunas, as has sometimes been 

 suggested, but are a western extension of the faunas of the New York province. At the "Bake 

 Oven" section the fauna of the lowest beds is of an age corresponding to the lower portion of 

 the Upper Helderberg period, while the uppermost faunas are of Hamilton age. The line of 

 demarcation between the Upper Helderberg and Hamilton faunas can not be exactly drawn. 



Personal communication. , 



