66 MEMOIRS OF THE CARNEGIE MUSEUM 
but in no considerable abundance. It will be noticed from the above remarks 
regarding the location of the several quarries worked in this region by Professors 
Marsh and Cope, that the quarries operated by Marsh were in a distinctly lower 
horizon than those from which Cope secured his material. While Professor Cope’s 
material all came from near the summit of the Atlantosawrus beds, that of Professor 
Marsh was derived from the lower members of those beds, certainly not more than 
100 to 150 feet above the Red Sandstones. This difference in horizon, which can 
be represented by scarcely less than 300 to 350 feet of sandstones and shales, must 
of necessity represent an enormous time interval, much greater perhaps than is 
ordinarily represented by sedimentary deposits of an equal thickness, for from the 
Fic. 28. View from near Cope quarry with the ‘‘ Nipple’’ in the middle foreground and Cooper 
Mountain in the distance. Garden Park lies in a depression about 600 feet below the ‘‘ Nipple’’ between 
the crest of the bluff, indicated by the line of trees on either side of the ‘‘ Nipple,’’ and Cooper Mountain. 
manner in which the sandstones and shales replace one another both laterally and 
vertically, and from the frequent examples of cross-bedding and ripple-marked sur- 
faces exhibited by the sandstones it is evident that the region was not one of con- 
tinuous and universal deposition, but that degradation and aggradation were in 
simultaneous operation and that while on the whole the latter agency predominated 
there may have been and doubtless were considerable intervals during which erosive 
agencies were the more efficient of the two. As should be expected the enormous 
time interval which elapsed between the deposition of the sandstones of the Marsh 
quarry and the shales of the Cope quarries, some 350 feet higher, was sufficient to 
