CHARACTER OF PALEONTOLOGIC EVIDENCE 301 



what similar cycads liave been found in beds which are ahnost certainly 

 Gomanchian, so the cycads can not be used to finally determine this 

 (question. The relation of the age of the Morrison formation to that of 

 the Potomac beds of the East and of the Kootenie in the West is impor- 

 tant. The lower member of the eastern Potomac carries a flora which 

 is very similar to that of the Kootenie in Montana, and the Kootenie 

 flora, as pointed out by Berry, is closely related to the other well known 

 Comanchian floras. Geologically the stratigi'aphic relations certainly 

 appear to favor Lower Gretaceous, or Gomanchian, age for large portions 

 of tlie Morrison. 



Phases of Problem, to v^^hom Assigned 



1 have attempted by way of introduction to very clearly state the prob- 

 lem in regard to the age of the Morrison and the three answers which 

 have been given to this problem. 



In the succeeding contributions to the symposium Mr. W. T. Lee, of 

 the United States Geological Survey, will apply the earth-movement 

 theory to the problem and treat the subject from the point of view of 

 the paleophysiographer. 



Dr. Gharles G. Mook, of the American Museum of Natural History, 

 will point out the vast area of the Morrison formation, its variations in 

 thickness and in lithological character, with reference to its mode of 

 (ii-igin and the general sources of the material of which the formation is 

 fomposcd. He Avill show that the actual age of the individual exposures 

 of the Morrison formation in one locality may differ considerably from 

 the age of the formation in another locality. 



Prof. E. S. Lull, of Yale University, will characterize the Sauropoda 

 and Stegosauria of the Morrison, pointing out their means of migration 

 and comparing the three great regions in which Sauropoda have been 

 discovered, namely, the Morrison of America, the Oxfordian to the 

 Wealden of western Europe, and the beds at Tendaguru in East Afj'ica. 

 Tiic African beds contain certain large and highly specialized dinosaui's 

 {Bracliiosaurus) similar to those in the Morrison; they are also reported 

 to be partly associated with or underlying Jurassic (Kimeridgian, Ox- 

 fordian) marine invertebrates. 



Finally, Dr. T. W. Stanton, of the United States Geological Survey, 

 will treat the subject rather from tlie invertebrate paleontologic stand- 

 point ill a comparison of the Morrison and the Gomanchian in relation 

 to the overlying and nndcrlying formations in various parts ol' the west- 



ern region. 



