1G4 ANNAL,^ NEW YORK ACADEMY OF fiCIENCEH 



4). Few unconformities of erosion. 



5). No extensive cross-bedding at high angles. 



6). A lacustrine rather than a land fauna or flora. 



The Morrison departs widely from every one of these six characteristics 

 except the last. The fauna might be considered lacustrine in part, but 

 some of it, if not most of it, is strictly terrestrial, and much of the aquatic 

 element may be fiuviatile as well as lacustrine. 



The series of events given by Riggs might fit very well a restricted area 

 of the Morrison deposits. The Morrison is an extremely widespread for- 

 mation, however, and this fact must be continually kept in mind in dis- 

 cussing its origin. There does not appear to be any evidence sufficient 

 for concluding that the lower beds of the Morrison are marine, and depo- 

 sition in estuaries is not in accord with the vast distribution of the for- 

 mation. 



There is abundant evidence for alternating lake and river conditions 

 in restricted areas, however, and no doubt such conditions were common. 



The statement by Loomis that tlie dinosaur bones had floated out to 

 sea by means of meat on them is not supported by the known facts, as 

 there is no evidence whatever of marine conditions in the Morrison for- 

 mation itself. 



Hatcher's theory of a low level plain, with lakes and interlacing 

 streams, fits the observed conditions much lietter. The interpretation 

 given in the present paper is in some senses an amplification of this idea. 



Preliminary Statement of Present Interpretation 



To the present writer the best explanation of the origin of the Morri- 

 son formation appears to be that of a number of large streams issuing 

 from a mountainous area and crossing a very broad flat plain. Such 

 streams would deposit much of their loads on their flood-plains in the 

 forms of very flat alluvial fans. Deposition by distributaries, aided by 

 tributaries and geolian action, would tend to unite these fans into a broad 

 alluvial plain. The main streams and tributaries consequent on the plain 

 would gradually extend such alluvial deposits over a very broad area. In 

 local basins between the principal stream areas and in abandoned stream 

 valleys lakes would probably form locally. In these lakes fine sediments 

 would 1)6 deposited, with sandstones around the margins. JRolian de- 

 posits would probably form to a certain extent between the main stream 

 areas also. 



The presence of a Comanchean sea in Texas and other areas east of the 

 Morrison area, shown by the presence of marine sediments, indicates that 

 part of the Morrison may be a true delta formation. 



