BURLINGTON GROUP. 69 



especially characterized by Pentremites roemeri. The Vermicular sandstone has a 

 thickness of 75 feet, and is ramified with irregular perforations resembling worm- 

 burrows. The Choteau limestone has a thickness of 100 feet, and was named from 

 Choteau Springs, in Cooper County. It has an extensive geographical distribution. 

 At Burlington, Iowa, the Group has a thickness of 77 feet, and consists of shales 

 and sandstones, capped by a four-feet bed of oolitic rock. It thins northerly until 

 it disappears. It has a thickness in Illinois of 200 feet, and at Kinderhook it con- 

 sists of grit-stones, sandy and argillaceous shales, with thin beds of fine-grained and 

 oolitic limestone. It has been identified in the Wahsatch Range, in Utah, and at 

 other places in the great West. 



$ 144. The fauna, on the whole, has assumed a Carboniferous aspect, notice- 

 able in the species which pass to higher Groups, and more strongly in the genera of 

 fish remains. Fossils having a wide distribution and characteristic species are Pro- 

 ductella concentrica, Producing cooperensis, Spirifera carteri, S. extenuata, S. pecu- 

 liaris, Syringothyris halli, Athyris hannibalensis, Rynchonella hubbardi, R. missouriensis, 

 Centronella allii, Bellerophon cyrtolites, Grammysia hannibalensis, Orthoceras in- 

 diamme, Goniatites oweni, G. marshallensis, and Phillipsia doris. 



CHAPTER XXVII. 



BURLINGTON GROUP*. 



145. THIS Group was named from Burlington, .Iowa, where it was called the 

 Burlington limestone before it was described as a geological subdivision. No single 

 geologist seems to have established the Group, or to have introduced the name to 

 science, though the first full definition is in the geological survey of Iowa for 1858. 

 The limestone at Burlington is subcrystalline, often friable, and largely composed 

 of crinoidal remains, has a thickness of 100 feet, and thins out northwardly. It 

 increases in silicious matter toward the top, until the limestone merges into silicious 

 beds, which, without evidence of unconformability, separate it from the Keokuk 

 Group. Hall referred these cherty layers to the Keokuk, but White, Wachsmuth, 

 and others refer them to the Burlington. In its southern extension, the Group 

 dips below the bed of the Mississippi, and rises again at Quincy, and furnishes a 

 fine exposure at Hannibal, Missouri. It exists in nearly every county on the 

 Mississippi, from St. Louis to Iowa, and west from St. Charles to Howard County, 

 and at Sedalia. The thickness varies from 100 to 500 feet. From a collection of 

 fossils received from Prof. Cope, the author identified the Group in the Lake 

 Valley Mining District of New Mexico; and it doubtless exists at other places in 

 the great West. 



146. The separation of the Burlington from the Keokuk could not be main- 

 tained were it not for the great change in the specific characters, of the Crinoids, 

 and this resulted probably from the deeper, or clearer, or less disturbed water in the 

 western localities during the Burlington period, than existed in the eastern locali- 

 ties. The detrital material may have prevented the recognition of the Group in 

 the Appalachian system, and rocks of the same age in Ohio, Kentucky, Indiana, 

 and other States may be referred to the Waverly or the Keokuk. In no other 



