HOLLAND AND PETERSON: OSTEOLOGY OF THE CHALICOTHEROIDEA. 195 
firmly embedded in the matrix, had suffered more or less displacement. It is 
rarely that the bones are found collocated in their true order, though in some 
instances a dozen or more vertebre may occur in regular series, with the corre- 
sponding ribs attached to them, or the bones of an entire limb may be found in 
place. The region, at the time when the bones were deposited, was probably a 
great plain, traversed by a broad and shallow river, like the Platte, or the Missouri, 
subject at times to overflows. It was a region of flat alluvial lands, which may in 
the summers have been in part dried, leaving here and there pools of water to 
which the animals of the region resorted, as in South Africa at the present time 
herds of ungulates resort to such places. Any one who is familiar with the writings 
of C. J. Anderson and Gordon Cumming ean picture to himself the conditions. 
At these pools the beasts, which roamed over the wide plain, came to drink, and 
here they died, as the result of age, or as they fell under the teeth and claws of 
carnivora. It may also have been, as suggested by Mr. Peterson, that at this 
particular point there was a ford, or crossing of the river, much resorted to by 
migrating herds of animals, and here many, especially younger animals, were 
mired in quicksands, and drowned. I have observed an instance, not immediately 
at the quarries above described, but near by, where the vertical position of the 
limb bones in the matrix plainly suggested that the animal to which they had 
belonged had sunk into the sands and had thus been destroyed, leaving its bones 
at a later age to tell to the curious eye of the passer-by the story of the brief tragedy 
of its last hours. After a period of summer drought or after the cold of winter, 
which must likewise then, as it does now, have led to the death of multitudes of 
creatures, the rivers rose as the result of rains, or melting snows, and the waters 
swept the dried carcasses of the dead and sometimes those of animals, which, 
unable to escape from the floods, were drowned, into places where they were 
destined to lie and become part of the rocky deposits which were in process of 
formation. 
In the Agate Spring Quarry there is abundant evidence of the action of water. 
Many specimens indeed give no proof that they have been thus subjected to wear 
and attrition. This was true in the case of the skeleton of the large Moropus 
which is made the basis of this memoir. Its remains, though disarticulated, were 
not scattered far, and it was not a difficult task to decide that they belonged to 
one and the same individual. But on the other hand some of the bones found 
near by were more or less worn by water, especially those in the lower part of 
the fossiliferous stratum. _The large animal was found where it had lain down 
and died, other bones below it had plainly been previously washed to the spot 
