Marine animal life lingered over into the new and marshy conditions, while plants changed quickly, and the old varieties passed away.

Quite likely, the Cretaceous was before and the Tertiary after, and the Laramie during the Rocky Mountain revolution. It was the period of transition. Benton oysters found new expansion, then changed into large fresh water clams, ten inches long. Soft woods of prodigious growth, that made ligniteous coal, passed away, and hard woods took possession of the plains. The Hartville Island sank still more, and over the west the great pleistocene lake was spread.

Bones of the Eocene were caught and swept along by the rushing waters, and are to be found in these later days of science, in rifts and drifts at Agate, and in the Goshen Holes. The country east and west of the sinking island warped and cracked. Great fissures paralleling the island opened up. to be quickly filled with ooze and slime, now hardened into Brule clay. At the base of the Scotts Bluff mountain (there was no mountain then) and in the Ardmore country, the clay was warped and twisted and tilted, and caught mammoth turtles, and winged water bats in its toils, to hold them there forever.

The original horse, a dozen varieties of the hippos family, from tree climbing horses and five toed ponies eighteen inches high, to the almost modern horse, left skeletons in the Agate fields. And there are bones of giant hogs,

HISTORY OF WESTERN NEBRASKA

that once wallowed in the marshes of White river, and duck-billed dinosaurs that crawled awkwardly through the water and mud. Croaking amphibious monsters, sprawled in mud and sand, or coiled under dripping trees, or splashed in shallow waters, in search of food, and wrote dumb tales of the Pliocene on the rocks.