BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 12, pp. 165-172, PLS. 13-18 APRIL 16, 1901 



SAND CIIYSTALS AND THEIR RELATION TO CERTAIN 

 CONCRETIONARY FORMS ^^ 



BY KItWIN HINCKLEY BARBOUR 



(Presented before the Society December 29, 1900) 

 CONTENTS 



Page 



Location and geological relations 165 



Mode of occurrence 106 



Physical characters of the concretions 166 



Material from Devil Hill region 167 



Analyses 170 



Microscopy and crystallography 170 



Location and Geological Relations 



Concretions of various kinds are abundant in several formations in 

 the Great Plains region, and their prominence is so marked that facts 

 which throw light on their origin are greatl}^ to be desired. Recently 

 there has been discovered in one of the Tertiary formations an exposure 

 which exhibits in a most instructive manner the development of con- 

 cretions by evident crystallization, which it is the purpose of this paper 

 to describe. 



The Tertiaiy of the Great Plains region comprises the White River 

 group of the Bad lands, mainly of Oligocene age, and a great series of 

 deposits which originall^^ were included under the term Loup Fork. 

 The greater portion of this series, extending through Nebraska into South 

 Dakota, has been separated by Darton under the designation of Arikaree 

 formation. It is believed to be of Miocene age. This formation consists 

 mainly of sand which locally is consolidated more or less, but is in part 

 loose and incoherent. The isolated portions give rise to many of the 



* Acknowledgments are due to the Honorable Charles H. Morrill, whose generosity made this 

 investigation possible. 



XXV— Bum,. Geol. Soc. Am., Vol. 12, 1900 (165) 



