SOME CAVERN DEPOSITS IN WEST TEXAS 155 



that the filling represents a time when the Cretaceous sediments were still 

 present over a part of this region. 



This is one of the few instances that have come under my observation, 

 where cavern deposits of such size have been penetrated by borings and where 

 it has been possible to identify them as such. Another instance the present 

 writer had occasion to describe was in the Silurian in the Atlantic Brewery 

 well drilled in Rock Island, Illinois. In this case it was clear, however, that 

 the age of the deposit was that of the base of the overlying formation, the 

 Pennsylvanian, and the filling itself in this case was quite ancient. 3 The find- 

 ing of. this last deposit in the Sayles well gives a satisfactory explanation of 

 the deposit found in the Rustler Springs formation in the Troxel well, already 

 referred to. The associated materials in which the Cretaceous fossils were 

 found were also, in that case, such as to suggest a cavern deposit, although 

 this was not recognized at the time the first examination of these borings was 

 made. 



Presented by title in the absence of the author. 



PALEOZOIC-MESOZOIC CONTACT THROUGHOUT WYOMING 

 BY S. H. KNIGHT x 



Presented extemporaneously. 



• STRATIGRAPHY OF THE LOWER OREODON BEDS OF THE SOUTH DAKOTA 



BIG BADLANDS 



BY WILLIAM J. SINCLAIR 



{Abstract) 



The Oreodon beds (Middle Oligocene) in the Big Badlands rest with ero- 

 sional unconformity on the Titanotherium beds (Lower Oligocene) and con- 

 sist of clays, often color-banded, of which the lower 40 feet, more or less, are 

 of pinkish-gray color. The so-called "Turtle Oreodon layer," or "Red layer," 

 of collectors constitutes the Mesohippiis bairdii-Orcodon culbcrtsoni zone par 

 excellence. 



In its upper part there is a zone of rusty nodules, usually but a few feet 

 thick, which is believed to owe its origin to ground water rising surfaceward 

 by capillarity, at times of decreased precipitation and more intense surface 

 evaporation, and depositing its limy content in the clays, at or near the sur- 

 face, either with or without an organic center for the nodules. This sup- 

 posedly climatically controlled horizon is constant in position over an area 50 

 miles and more across and has been used by the Princeton 1920 and 1921 

 expeditions as a datum plane for faunal and stratigraphic studies. A second, 

 quite narrow zone of nodules lies some 60 feet higher than the one first men- 

 tioned and seems to be similar to it in origin. Both are richly fossiliferous, 

 but the second has not been traced orer so great an area as the first. 



3 J. A. Udden : An account of Paleozoic rocks explored at Rock Island and vicinity. 

 19th Annual Report of the U. S. Geological Survey, part 2, pp. 820-840. Compare also 

 Geology of Iowa, James Hall, vol. i, p. 130. 



1 Introduced by James F. Kemp. 



