HELDERBERGIAN OF THE UNITED STATES 273 



Until recently no other region for these strata was known south or 

 west of Tennessee and eastern Missouri. In 1891 Mr Hill discovered 

 and Professor Williams identified the Helderbergian in Indian Terri- 

 tory. The fauna there contains 40 species, and is given in another place 

 on the authority of Doctor George H. Girty.* Mr Taff describes the In- 

 dian Territory outcrops as follows : 



" Rocks of Lower Helderberg period, as far as known in Indian Territory, are 

 limestones and occur in the Chickasaw Nation, near its east line, in townships 1 

 south, range 8 east, 2 south, range 8 east, and 1 north, range 7 east. The second and 

 third localities are known from a few fossils collected from highly tilted limestones 

 found between black shale which is unconformably disposed above and thicker 

 beds of Silurian or Ordovician limestone resting below. The limestone in these 

 two localities, the one upon the south side and the other upon the north side of 

 an extensive area of Silurian and Ordovician limestone, bears westward through an 

 unknown distance in the Chickasaw Nation. The Lower Helderberg in township 

 1 south, range 8 east, is in the Atoka quadrangle and has been surveyed and 

 mapped. It occurs at the east end of an extensive area of limestone and sand- 

 stone, part of which is known to be Lower Silurian and Ordovician. This area of 

 Lower Helderberg limestone is 4J miles long north and south and is from \ to 2\ 

 miles wide. The beds dip eastwar atd a low angle, and are overlain unconlorm- 

 ably upon the north, east, and south sides by black fissile shale, which includes 

 beds of flint, chert, and limestone segregations. 



" The collection of Lower Helderberg fossils discussed by Doctor G. H. Girty in 

 the Nineteenth Annual Report of the United States Geological Survey were taken 

 from this locality. The reference of these rocks to the Lower Helderberg is based 

 upon and due to Doctor Girty's work. 



" The Lower Helderberg limestone has an estimated thickness of 140 to 200 feet, 

 and its strata may be divided into two and possibly three stratigraphic units. 

 While the contrast between these units is not very great, it is sufficient to induce 

 description. (1) From the highest stratum in contact with the black shale down- 

 ward through 95 feet the beds are light yellow or white limestone, which are 

 occasionally separated by marly layers. Many of these limestone strata contain 

 flint and cherty concretions. In almost all the beds remains of fossil shells were 

 observed, and many especially which contain chert and flint bear shells beauti- 

 fully preserved in chalcedony. (2) Next below there are 50 feet of friable layers 

 of yellow limestone interstratified with still softer marly beds. These beds are 

 very fossiliferous, abounding in well preserved corals, trilobites, and brachiopods. 

 (3) Continuing downward through 55 feet thicker beds of crumbling limestone are 

 encountered, which have yielded no well preserved fossils. Some of these beds are 

 granular limestone and contain fragments of fossils. These, as suggested by Doctor 

 Girty, may prove to belong to the Niagara period, as do the beds immediately 

 below. 



"The rock below these non-fossiliferous beds is a massive, whitish, silicious, 

 oolitic limestone 15 to 30 feet thick. It has yielded but few fossils and these Doctor 

 Girty refers to types more nearly related to the Niagara than to the Lower Hel- 

 derberg period. 



♦.Nineteenth Ann. Rep. U. S. Geol. Survey, 1899, pp. 546-550, 552-573. 

 XL— Bull. Geol. Soc. Am., Vol. 11, 1899 



