•mot.] PHYSICAL GEOGRAPHY OP THE REGION, 2fi3 



with an abrupt escarpment toward the southeast. The Cumberland 

 plateau is a belt of such tables. It is thus a connecting link between 

 the Appalachian mountains and the interior plain, but it is not every- 

 where to be recognised. <>n the line of the out ward journey it is not 

 discriminated. On the line of the return journey it is represented by 

 the Oatskill mountains, which are visible in the distance from the west 

 (right) side of the train as it follows the Hudson River. 



The central plain of the continent does not yield a simple and defi- 

 nite classificat ion into physiographic provinces, but the portion tra- 

 versed by the excursion may be imperfectly characterized by describ- 

 ing three topographic types which it illustrates: the Lake region, the 

 Prairie region, and the Great plains. The hake region 2 isarather 

 uneven plain, having for its foundation, at the north, crystalline rocks 

 of complex Structure which are so degraded that all mountains are 

 Obliterated, and at the south. Paleozoic rocks, level or gently folded, 



and likewise degraded to approximate evenness. Over these are 



deposits Of glacial drift, irregularly disposed so as to break the surface 

 into ;i large number of basins, holding lakes, lakelets, ponds, and 

 swamps. 3 On the outward jonmey this region is traversed in the 



States of Ohio, Indiana. Illinois, Wisconsin, Minnesota, and a pari of 



North Dakota: on the ret urn journey, in Illinois. Indiana, Michigan, 

 Canada, and western New York. 



The Prairie region is less susceptible of mapping than most other 

 divisions, because it depends on complex conditions involving climate 



as well as surface configuration. Humid lands are normally charac- 

 terized by forest and are suited for agriculture; arid lands are nor- 

 mally characterized by the absence of forest, and are unsuited for agri- 

 culture without irrigation. The normal distribution of forest is modi- 

 fied by fire, as annual fires destroy forests but permit the growth of 

 grasses. In regions of great humidity a forest tire does not Bpread 

 with facility; in regions of rugged surface it is limited bytopographic 

 accidents: in regions of moderate humidity and smooth surface a forest 



is destroyed by tire, and thus a fertile region becomes hare of trees 



and is clothed by grasses. The outward journey traverses prairie in 



western .Minnesota and adjacent North Dakota. A typical portion of 

 the prairie belt is traversed on the return journey in .Missouri. Iowa, 

 and Illinois. 



The Great plains slope eastward from the eastern foot of the Rocky 

 mountains, descending from altitudes of 5,000, 6,000, and 7, (too feet 



1,500, 1,800, L'.H'O m.) nearly to sea level. In detail the surface undu- 

 lates gently and is devoid of commanding eminences, except that the 

 Ozark' uplift has produced low mountains in Texas. Arkansas, Indian 

 Territory, and Missouri; the Black Hills uplift* has produced another 



group at the western edge of South Dakota: and a few buttes. mostly 



