GENERAL GEOLOGICAL FACTS AND PRINCIPLES. 9 



Devonian ; Lake Ontario, by Silurian. Running -south through 

 Ohio, we find an important fold known as the Cincinnati uplift, 

 with a north and south axis. It was elevated at the close of the 

 Lower Silurian. In the lower peninsula of Michigan and in eastern 

 Ohio and western Pennsylvania the Carboniferous is extensively 

 developed. 



V. Mississippi Valley. The head waters of the Mississippi 

 are in the Archaean. It then passes over Cambrian and Siluiian 

 strata in Minnesota, Wisconsin, northern Iowa, and Illinois, which 

 in these States lie on the flanks of the Archaean " Wisconsin 

 Island" of central Wisconsin. These are succeeded by subordi- 

 nate Devonian, and in southern Iowa, Illinois, and Missouri by Car- 

 boniferous. In southern Missouri the Lower Silurian forms the 

 west bank. Thence to the Gulf the river flows on estuary deposits 

 of Quaternary age, with Tertiary and Cretaceous farther inland. 



VI. Gulf Region. The Gulf States along the water front are 

 formed by the Quaternary. This is soon succeeded inland by very 

 extensive Tertiary beds, which are the principal formation repre- 

 sented. 



VII. Prairie Region. West of the Paleozoic rocks of the 

 States bordering on the Mississippi is found a great strip of Creta- 

 ceous running from the Gulf of Mexico to and across British 

 America, and bounded on the west by the foothills of the Rocky 

 Mountains. A few Tertiary lake deposits are found in it. Quite 

 extensive Triassic rocks are developed on the south. The surface 

 is a gradually rising plateau to the Rocky Mountains. 



VIII. Region of the Rocky Mountains, the Black Hill 9 and 

 the Yellowstone National Park. The Rocky Mountains rise from 

 the prairies in long north and south ranges, consisting of Archaean 

 axes with the Paleozoic in relatively small amount, but with abun- 

 dant Mesozoic on the east and west flanks. In the parks are found 

 lake deposits of Tertiary age. There are also great bodies of igne- 

 ous rocks, which attended the various upheavals. The principal 

 upheavals began at the close of the Cretaceous. The outlying 

 Black Hills consist of an elliptical Archaean core, with concentric 

 Paleozoic and Mesozoic strata laid up around it. The National 

 Park consists chiefly of igneous (volcanic) rocks in enormous 

 development. 



IX. Colorado Plateau. The Rocky Mountains shade out on 

 the west into a great elevated plateau, extending to central Utah, 

 where it is cut off by the north and south chain of the Wasatch. 



