ENVIKONMENT OF THE TITANOTHEKES 



Geologic succession of Oligocene titanoiheres in the Chadron formation — Continued 



115 



HATCHER'S COHECTIONS, 1886-1888 



According to a report delivered orally by Hatcher to 

 the author in 1901, the collections made by him in 1886 

 included 24 skulls, some from Hat Creek, Nebr., and 

 some from the Big Badlands of South Dakota, which 

 were designated in his records and field notebooks by 

 the letters A, B, C, etc., but which now bear United 

 States National Museum numbers. In 1887 Hatcher 

 collected from Sioux County, Nebr., mostly from Big 

 Cottonwood Creek (adjoining Hat Creek), a second 

 series of skulls, which he similarly designated by the 

 letters A to K. Later in the same season he moved 

 camp to the South Dakota Badlands and collected the 

 skulls L to Z and a to w. Thus during the season of 



1887 he collected 45 skulls. During the season of 



1888 he collected another series of 24 skulls in the 

 South Dakota Badlands, which he designated by the 

 letters a', b', c', to z' but which Professor Marsh 

 later relettered A' to Z' . Subsequently the catalogu ers 

 of the United States National Museum assigned 

 numbers to all these skulls. These revisions of the 

 records have caused confusion, so that it is now doubt- 

 ful whether certain skulls that bear capital letters and 

 United States National Museum numbers belong to 

 the series of 1886 from Hat Creek, Nebr., or to the 

 series of 1887 from Big Cottonwood Creek and the 

 South Dakota Badlands. Such uncertainty, of course, 

 involves equal uncertainty as to the localities and 

 geologic levels at which the specimens were obtained, 

 but nearly all uncertainties have been settled by Dr. 

 W. K. Gregory through careful examination of all 

 the available evidence, with the assistance of Mr. 

 J. W. Gidley, of the United States National Museum. 

 The above table is based on these original and revised 

 records. 



This remarkable collection, now preserved in the 

 United States National Museum, constitutes the 

 reference standard as specifically determined by the 

 author with the assistance of Messrs. Gidley and 

 Gilmore and includes the skulls and jaws indicated 

 below, which are enumerated in detail under the 

 respective genera in Chapter VI : 



Allops phylum: 24 skulls and lower jaws in four specific stages. 

 Diploclonus phylum: 1 skull in one specific stage. 

 Brontops phylum: 58 skulls and jaws in three specific stages. 

 Brontotherium phylum: 42 skulls and jaws in nine specific 



Megacerops phylum: 7 skulls and jaws in three specific stages. 

 Menodus phylum: 26 skulls and jaws in four specific stages. 



Figure 76. — Section showing the results of stratigraphic 

 leveling in the Chadron formation (Titanotherium zone) in 

 the badlands of White River, S. Dak., in June, 1901, by 

 N. H. Darton 

 The results are affected by dip, by unconformity, and by variation in the thickness 

 of the beds. In determining the dip the beds showing the nearest reliable con- 

 tacts of the Chadron with the Pierre formation were selected for all the levelings, 

 and as most of the distances determined were short and were measured along the 

 strike of the low-dipping beds the angle of the dip is unimportant . The Chadron 

 formation lies on a smooth plane of unconformity, and its basal member is gen- 

 erally continuous but was doubtless laid down against a sloping shore, and the 

 layers are not synchronous throughout its extent. Nearly all the bones listed in 

 the text, however, were found in an area so small that this unconformity is unim- 

 portant. The variation in the thickness of beds is the most important factor 

 aflecting the determination of the stratigraphic levels and one that could not be 

 accurately determined, for the beds present so much variation in character that 

 they can not be followed for a distance long enough to afford a basis for strati- 

 graphic subdivision of the formation. A horizon 30 feet above the base of the 

 formation at one point may represent a horizon 45 feet above it at another point; 

 thus a bone found at A may have been deposited at the same time as a bone 

 found at B. 



