28 



the Magnolias, Platanits, Populug, Sali.r, and Menispermites, the essential 

 types of the vegetation of the Dakota group being, therefore, those of low 

 islands or of low shores, rather than of hills and dry land. 



&5. — DISTRIBUTION OF THE LEAVES IN THE COMPOUNDS OF THE DAKOTA GROUP. 



Professor Capellini remarks, in his introduction to the pamphlet on the 

 Phyllites du Nebraska: "Although the Tekamah molasse is distinctly strati- 

 fied, the vegetable impressions are not arranged in the plaue of stratification ; 

 a proof that the water wherein were deposited the materials which entombed 

 the leaves, and which were brought by alluvion, was not quiet enough. The 

 deposit was not made quietly enough to allow the leaves to be flattened as 

 well as those which are found in the deposits of Oeningen and of Senigallia." 

 The fact stated by the European professor is not generally observed. The 

 leaves, indeed, are found sometimes rolled or crumbled as may have been 

 dry leaves when falling upon a muddy surface where they may have been 

 imbedded in that condition, and often, too, penetrating the mud edgewise, 

 either vertically or in various degrees of inclination to the plane of the mud 

 deposits; at some places they have been also probably rolled by the waves. 

 But these deviations of the horizontal plane are far from frequent. In most 

 cases the leaves are flattened upon the shales, often found covering each 

 side of a piece of shale of moderate thickness, and also when in abundance 

 they are generally superposed and flattened upon another. This devia- 

 tion of the horizontal plane is nowhere more marked for the fossil plants of 

 the Dakota group than for those of our Carboniferous or of our Tertiary 

 formation, and it appears rather ascribable to wind or to tidal action than to 

 any current or alluvial movement. These remarks already tend to indicate 

 that the Cretaceous fossil leaves have been derived from trees or groups of 

 trees growing in the vicinity of the muddy bottoms where they have been 

 buried and fossilized. Other facts confirm this assertion. 



The leaves are regularly disseminated in the shale of this formation, and 

 thus found here and there over wide areas. They are often very abundant 

 at one locality, occupying a surface of small extent, and then they disappear 

 entirely from the same horizon and are not seen anywhere around for miles. 

 The locality near Salina, from which a large number of fine specimens have 

 been obtained, covers scarcely three acres of ground. In following the bluffs 

 to the station for a distance of about eight miles, although the exposures of the 



