IOWA ACADEMY OF SCIENCES. 135 



the interbedded lignite. The cross-bedded sandstone 

 which passes gradually into clay; the clay beds that are 

 sometimes remarkably persistent in color and texture, and 

 at other times extremely variable, passing abruptly into 

 carbonaceous clay and on into lignite; the large tree trunks 

 that are scattered through all of the clay beds; all suggest 

 the former presence of shifting lakes fed by streams laden 

 with silt and timber. In one instance stumps three and 

 four feet in diameter and fifteen feet high, silicified, were 

 found over an extensive area standing upright. They 

 were not associated with a lignite bed, and seem to repre- 

 sent part of a forest that was silted under by the shifting 

 of a lake bed. 



This view of the origin of the lignites is admittedly 

 hypothetical. It seems, however, to present a reasonable 

 line for study, to form a working hypothesis, to use the 

 admirable term of Professor Chamberlin. To prove or 

 disprove it, additional study will be directed to the follow- 

 ing points: To determine whether the Laramie of the 

 mountains is older than that of the plains; to show 

 whether in the main the wood from which the lignite was 

 derived was of land growth and to determine the habitat 

 of the species, and to see what light the fauna of the Lar- 

 amie throws on the relation of land to water at that time. 



