106 THE UNIVERSITY SCIENCE BULLETIN. 



The bottom of the ravine containing the tracks scales off more 

 readily than the surrounding bluffs and is consequently rapidly 

 eroding away. The banks of the ravine are very steep, the average 

 width at the bottom being about 3 feet, with a width at the top of 

 25 feet, while the depth from the level of the banks above to the 

 level of the tracks is 25 feet. 



CORRELATION OF FORMATION. 



The heavy sandstone rocks in which the impressions appear are 

 exposed in a sharp escarpment on the south side of the Wakarusa 

 creek for a distance of 1% to 2 miles, in varying heights ranging 

 from a thin feathering edge to 40 feet. The highest point is attained 

 in close proximity to and just above the small ravine in which the 

 tracks were discovered. 



A short distance southw^est, at the extreme eastern end of Blue 

 Mound, and just above these exposures, an outcrop of the latan 

 limestone occurs, thus definitely placing the sandy exposures in the 

 division which composes the lowest member of the Douglas forma- 

 tion, and as it occurs immediately below the latan limestone con- 

 stitutes a part of the uppermost strata of the Weston shales. 



The inclusion of this heavy sandstone in the Weston shales will 

 be better understood by referring to the description of the Douglas 

 formation by Moore (5) : 



"The shale members of the Douglas are variable in composition and texture, 

 changing markedly from point to point. In the north there is a predominance 

 of clay shales, which is sufficiently pure for use in brick manufacture, but 

 towards the south the proportion of sand is notably increased. In places here 

 the shale is replaced by thick, massive sandstones. Coal occurs at one or two 

 horizons in the formation, but is not of great thickness and has been worked 

 only locally." 



DESCRIPTION OF TRACKS. 



Tkack No. 1, the first in the series, shows clearly where the front 

 foot had pressed down in the soft, plastic mud to a depth of eight 

 inches, leaving at this level a well-defined ledge. Immediately be- 

 hind this narrow ledge the superimposed hind foot had pressed 

 down to a depth of another seven inches, plainly indicating that the 

 animal was of large size and great weight. This impression repre- 

 sents the tracks of the front and the hind foot of the left side. 



Track No. 2. (Plate I, fig. 2.) This track was located 12 feet 

 from No. 1 and is one of the finest in the set, showing distinctly the 

 impressions of five bluntly pointed toes. Between the toes the 

 weight of the animal has caused the mud to ooze up, not in sharp 



