Page:A Brief History of South Dakota.djvu/15

 A BRIEF HISTORY OF SOUTH DAKOTA

CHAPTER I

is very easy to read the story of the rocks in South Dakota, for here more than anywhere else the several formations are exposed to view: and we can readily see what must have happened in that time very long ago, before men, or even animals, inhabited the Dakota land. The rock formations can be seen more or less all over the state, but their story is clearly shown especially in that section near the head waters of the White River at the foot of the Black Hills, known as the Bad Lands.

We learn there that in an ancient time a great ocean rolled over South Dakota; that some great convulsion must have occurred deep in the earth which threw up the Black Hills and other western mountains; that the ocean swept over these hills, grinding them up and washing them down across its floor toward the eastern part of the state, thus laying down a formation or stratum now compressed into hard rock which is the lowest of the many formations studied by the geologist. We learn that again and again the rocks and hills were raised up, each time to be 9