BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 26, pp. 315-322 AUGUST 17, 1915 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



OEIGIN AND DISTRIBUTION OF THE MORRFSON 



FORMATION ^ 



BY CHARLES C. MOOK 



(Read In'.forc lite Piileoniolo<jical Soeieli/ Dcct'.nthcr "0. lOJ'j) 



CONTENTS 



Page 



Introduction 315 



Distribution and thickness of the Morrison 316 



Criteria for determining tlie origin of the formation 317 



Conclusions 319 



Introduction 



The age of the Morrison formatiou is necessarily bound up with the 

 question of its origin and the physiograpliic conditions under which it 

 was deposited. The present paper is a study in this direction. The 

 writer was sent into the field in the summers of 1913 and 1914 by Prof. 

 H. F. Osborn to study the Morrison formation in connection with his 

 forthcoming monograph on the sauropod dinosaurs. Considerable time 

 has been spent in the winter of 1913-1914 and in the past fall in as- 

 sembling the results of this field study, together with a thorough study 

 of the literature of the subject. Some of the conclusions from these 

 studies are given in the present communication. The Morrison foi-ma- 

 tion is one of those series of beds which have been the subject of con- 

 siderable controversy. By the workers on the Hayden and other early 

 surveys they were known as "variegated beds/' Jurassic beds, Dakota 

 beds. Lower Dakota beds, Atlantosaurus beds, and in pai't Flaming Gorge 

 formation. Later they have been known locally as the Beulali shales, 

 Como beds, McP'lino Ix'ds. and (iinuiison formation. These local names 



1 Contribution to tlio symposium held at the Philadelphia meeting of the Society De- 

 cember .".0, 1014. 



Manuscript received by the Secretary of the Society April 3, 1915. 



(315) 



