18ft6.] 295 [Ilayden. 



amination, who, after u careful study of them, aflBrmed that these 

 rocks are Cretaceous. Thus a long-disputed point has been set at 

 rest. 



The vegetable remains of this formation are peculiarly interesting 

 to the geologist, from the fact that among them are forms so closely 

 resembling the leaves of the fruit and forest trees of the present 

 time, — a very marked and important advance in the progress of the 

 vegetation of the ancient world. So far as can be seen from the 

 collections already made, they do not seem to exhibit as high a type 

 of organization as those of the same class of the present day. There 

 seem to be no serrations on the edges of the leaves or other attempts 

 at ornamentation, which are so finely shown in those of our living 

 forest trees. The inference is, therefore, that this flora illustrates the 

 great law of progress : commencing with great simplicity of form, 

 and advancing, step by step, to greater complexity and beauty. 



Dr. H. also spoke of the interesting fossils he had collected during 

 the past season from the Fort Pierre group, at Sage Crock and other 

 localities in that vicinity. . These fossils are so abundant at certain 

 localities, extending in continuous lines or belts for long distances 

 across the country, and so well preserved, that one might regard 

 these shell zones as the shores of the great Cretaceous sea. 



Dr. H. also exhibited some thin slabs of fine-grained ferruginous 

 sandstone, from the head-waters of the Teton River, eastern side of 

 the Bad Lands. They belong to the upper part of the Fox Hills 

 group, near the close of the Cretaceous period of .the Upper Mis- 

 souri. They were covered with very distinct trails of gasteropoda 

 and marine worms. These specimens seem to indicate a shore-line, 

 from which there was an ebb and flow of the tide, and as the waters 

 receded these little animals left behind, would struggle over the soft 

 sand toward the water, leaving their peculiar trails, which would be 

 filled up with sediment by the returning tide. 



The fact of the existence of four and perhaps five great fresh-water 

 lakes in the Upper Missouri country during the Tertiary period, is a 

 matter of the highest interest, and it is our privilege to collect all 

 the evidence possible, and thus restore to our minds the ancient 

 physical geography of this region. We cannot doubt that during all 

 the difl'erent geological epochs there were lakes, rivers, seas, and 

 oceans, islands, continents, and mountains, and that it is the most 

 important mission of the geologist to restore the physical geography 

 of these difl^erent epochs to the eye of science. 



YOh. X. — 2o 



