164 
W. N. THAYER 
formerly had while the old surface was being subdued. The Sacra- 
mento and Columbia rivers are prominent examples of this type. 
TABLE TO EXPLAIN THE ACCOMPANYING MAP 
Major divisions, the strongly characterized parts of the continent, are separated by heavy lines, and 
are distinguished by Arabic numerals; Provinces are separated by light lines, and are distinguished by 
letters; sections are distinguished by Roman numerals. 
Major Divisions 
1. Laurentian Plateau 
(a) 
(b) 
(c) 
(d) 
Province 
Section 
Laurentian Plateau proper 
Superior Highlands 
Adirondack Mountains 
Unnamed 
2. Atlantic Plain 
(a) 
(0) 
Continental shelf 
Coastalsblainmeer eee 
. Atlantic section 
. Gulf section _ 
. Yucatan section 
3. Appalachian Highlands 
Piedmont region 
Blue Ridge Mountains 
Appalachian Valley 
St. Lawrence Valley 
Appalachian Plateaus 
New England region 
4. Interior Plains 
Interior Low Plateaus 
Central Lowland........ 
Great Plains 
Wyoming Basin 
Texas Hill region 
Canadian Great Plains 
Anatuvuk Plateau 
I. East. Lake section 
. West. Lake section 
. Driftless area 
. Till plains 
5. Interior Highlands 
Ozark Plateau 
Ouachita region......... 
I. Arkansas Valley 
II. Ouachita Mountains 
6. Rocky Mountain System 
Southern Rockies 
Boundary group 
Mackenzie Mountains 
Endicott Mountains 
7. Intermontane Plateaus 
Columbia Plateau 
Colorado Plateau 
Basin-and-Range province 
Interior Plateaus 
Yukon Plateau 
8. Pacific Mountain System 
(f) Sonoran Desert 
(g) Anahuac Desert Plateau 
(hk) Sierra Madre 
I. Sierra Nevada 
(a) Pacific Mountains....... II. Cascade Mountains 
III. Coast Range of British Columbia 
IV. Coast Range of Alaska 
Pacific Border province... 
Coast Ranges........... 
I. California trough 
. Puget trough 
. Copper River basin 
I. California-Oregon-WashingtonRanges 
. Alaskan Ranges 
9. Southern Mexican High- 
lands 
(a) 
(b) 
Volcanic province 
Sierra del Sur province 
to. Isthmian Lowlands 
=~ 
8 
LS 
Tehuantepecan province 
