WARD.] COLLECTIOX.S FROM THE FORT UXIOX GROUP. 543 



its iron oxidized, turning it bright red, so that it may be regarded as a 

 ferruginous marl ; tlie other is very calcareous, and may be classed as 

 an argillaceous limestone. 



The Iron Bluff stratum yielded a considerable variety of plant forms. 

 Besides the large Coccul us leaves, which were present in great abundance 

 (though, owing to their great size, usually in a fragmentary condition), 

 there occurred an immense quantity of stems of a gigantic Equisetum 

 and of monocotyledonous plants. One of the most striking features of 

 this bed was the occurrence almost everywhere of the stems of certain 

 plants marked all over with very distinct diagonal meshes or cross-lines. 

 These lines consist entirely of deeper colored fine streaks, crossing one 

 another with great regularity at a constant angle. They have the ap- 

 pearance of having wound spirally round the stems in two directions, 

 those of each set being all parallel to one another, and thus forming 

 little rhombs where the systems cross. There is no apparent elevation 

 nor depression, but the fine lines of deeper red are seen in cross-section 

 to penetrate the general surtace of light buff, showing that they possess 

 some thickness. The diagonal meshes thus formed vary very much in 

 size, from a millimeter to nearly two centimeters across, and this fineness 

 or coarseness seems to be approximately proportional to the size of the 

 stem on which it occurs. This structure first reminded me of the peculiar 

 cross-lines that occur in the broader stems of certain Monocotyledons, 

 such as Sagittaria, Eriocaulon,etc., and Heer has figured a fossil Sparga- 

 nium stem exhibiting such a structure. Cawlinites sjjarganioides of hes- 

 quereux ("Tertiary Flora," ])latexiv, figs. 4 and 10) exhibits something 

 faintly analogous to our plant, and Mr. Lesquereux has sought to ex- 

 plain the occurrence of the cross-lines ( p. 100 ). But the resemblance 

 is too distant to be of any service in the solution of the problem. Cer- 

 tain specimens showing a transition to the normal epidermis, with very 

 tine longitudinal striation, make it next to certain that the parts ex- 

 hibiting this structure are decorticated, and some evidence exists to 

 prove that the lines may represent the cell walls of the loose cambium 

 tissue of an exogenous j)lant. The peculiar mode of branching of some 

 specimens also suggests the exogenous rather than the endogenous 

 mode of growth. Certain it is that the diagonal meshes always occur 

 in connection with definite vegetable structure, and even should they 

 Ijrove to be themselves inorganic and to have no connection with the 

 tissues of the plants on which they occur, still the fact must remain 

 that they exist in consequence of such tissues, and are in so far of vege- 

 table origin. I leave the question unsettled for the present and in- 

 trust its solution to further research. 



The matrix in which the leaf prints found at Burns's Eanch are em- 

 bedded is an exceedingly fine-grained argillaceous limestone of a bluish- 

 gray color, weathering reddish-brown, and having no regular stratifica- 

 tion, but very brittle, and easily breaking at any point with conchoidal 

 fracture, leaving very sharp edges. The degree of friability is much in- 



