OF NORTH AMERICA. 59 



part of southeastern California, the extreme northwestern part of 

 Mexico and the whole of Arizona. 



9. GREAT BASIN. This includes the desert and arid regions of 

 Nevada, Utah, Oregon and California. There is no outward drainage. 

 A number of lakes occupy this basin, of which Great Salt Lake is the 

 largest. 



10. CALIFORNIAN. This area includes the coastal portions of 

 Oregon and California, as well as that portion of the states west of 

 the Sierra Nevada and Cascade ranges. The Sacramento and San 

 Joaquin are the principal river systems. Its southern extension reaches 

 the northern part of Lower California. 



11. Rio GRANDIAN. This includes the basins of the Rio Grande 

 and the Pecos River, with their tributary streams. It embraces the 

 southern part of Colorado, nearly the whole of New Mexico, the 

 western part of Texas and the northern and central parts of Mexico 

 drained by the tributaries of the Rio Grande. It includes the higher 

 Mexican plateau. 



12. UPPER MISSISSIPPIAN. This area includes the territory 

 drained by the upper Mississippi and Missouri rivers, including their 

 tributary streams. It embraces the country south of the "Height of 

 Land" in southern Canada and the Great Lakes, all of the territory 

 between the Rocky Mountains on the west and the Appalachian Moun- 

 tains on the east, and north of about the 35th parallel of north latitude. 

 The drainage areas of the Arkansas and Tennessee rivers form the 

 southern boundary of this area, and the line of the water partings 

 varies from the 35th to the 38th parallels. The Ozark Mountains also 

 mark the southern limits of a portion of this region. 



13. LOWER MISSISSIPPIAN. This includes the region south of the 

 Arkansas and Tennessee rivers. Its western limit is the Great Plains 

 east of the Rio Grande drainage. Its eastern limit is somewhat indefi- 

 nite, but would seem (judging by the distribution of certain Lymnseas) 

 to be north of the St. Johns River in Florida, where a line drawn north- 

 ward to the Appalachian range would separate the Lower Mississippian 

 from the Carolinian region. This region embraces the lower drainage 

 areas of the Mississippi River as well as all of the rivers flowing into 

 the Gulf of Mexico, east of the Rio Grande. It includes also the entire 

 peninsula of Florida. 



14. CAROLINIAN. This area includes all of the coastal strip east 

 of the Appalachian range from southern New Jersey south to the St. 

 Johns River, Florida. The drainage is into the Atlantic Ocean. Its 

 northern limit is marked by the Potomac River, whence the line of 



