302 H, P. OSBORN JURASSIC-CRETACEOUS TIME 



SUMMAKY 



When these contributions are published and can be carefully compared, 

 it will probably appear as the chief result of this symposium that the 

 intermediate theory is correct; that, as long ago suggested by Prof. S. W. 

 Williston, the Morrison sedimentation was a very comprehensive and 

 wide-spread process; that it began in certain localities earlier than in 

 others, namely, during Upper Jurassic times; that it extended well into 

 Lower Cretaceous times ; that all the sediments known as jMorrison rep- 

 resent a vast period of geologic time in which sedimentation was remark- 

 ably slow, because at no point does this so-called formation — which is 

 rather a stage or series of stages in the European sense — attain any con- 

 siderable thickness. The more primitive forms of Morrison life are 

 partly, at least, truly Jurassic, while the more specialized progressive 

 maybe are truly Lower Cretaceous. 



