12 Erwin H. Barbour, 



great underground stems arrest attention at once ; for 

 although the average diameter may be about eight or ten 

 inches, yet I measured one here — an immense log of a fossil, 

 some eighteen inches through. I have represented, in Figs. 

 6, 7, and 8, several forms noticed, and others will be seen in 

 Plates I., II., and III. Figs. 6, 7, and 8 show for themselves 

 certain peculiarities and enlargements. Fig. 8 represents 

 one thirteen feet long, with evidence of several feet more, 

 having at its upper end a great, knotted, wrinkled, irregu- 

 lar, sponge-like enlargement. These stems, so hard and so 

 easily distinguished from the imbedding matrix, begin toward 

 their extremities to graduate insensibly into the surrounding 

 sandstone, just as if before fossilization the "underground 

 stem," like modern ones, while growing forward, had rotted 

 in the rear. The walls of these stems, which are thick and 

 fairly solid and of a chalk-white color, encircle a core of 

 sandstone, perforated more or less by ramifying tubes and 

 tubules. 



In nearly all specimens the large tubes and cavities are 

 filled with an interesting deposit of gelatinous silicic acid, of 

 about the hardness and texture of paraffine or castile soap. 

 Occasionally this gelatinous silica is deposited in sheets five 

 to six inches wide by one and one-half inches thick, lying 

 medially and horizontally in the underground stem. Its color 

 ranges from aurora red to pink, blue, gray, and white, being 

 highly opalescent in some cases and dendritic in others. On 

 drying, the unbroken homogeneous mass is divided by shrink- 

 age cracks, and losing its color, becomes white. 



What added not a little to the difficulty of the whole prob- 

 lem was the discovery of a finely preserved rodent's skeleton 

 in the great stem of one specimen (Fig. 9). 



This rodent is about the size of a 'jack rabbit ' ; its incisors 

 are large proportionally ; sagittal and occipital crests high and 

 sharp ; shoulder girdle apparently mole-like. 



How or when it came there is explained perhaps by the 

 subsequent discovery of a massive fragmentary fossil cork- 

 screw, found in the bluffs bordering the Niobrara. It is 



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