LIST OF ILLUSTRATIONS. 



PLATES. 



PAGE. 

 Pl^TE 1. 



A. Stages of a sandhill sere as seen in three 



successive blowouts, Halsey, Ne- 

 braska 4 



B . Section of a peat deposit, ' ' Burton Lake, ' ' 



Lancashire, England, serving as a 



record of the cosere 4 



Plate 2. 



A. Bad lands and sand-bars. North Platte 



River, Scott's Bluff, Nebraska; bare 

 areas due to topographic initial 

 causes 6 



B. Ant-hill with zone of Munroa sguarrosa; 



a bare area due to a biotic initial 



cause 6 



Plate 3. 



A. Primary bare area, due to weathering. 



Mount Garfield, Pike's Peak, Colo- 

 rado 34 



B. Secondary bare area, due to wind erosion, 



Morainal Valley, Pike's Peak, Colo- 

 rado 34 



Plate 4. 



A. Lateral Moraine of the Illecillewaet 



Glacier, British Columbia 36 



B. Terraces and valleys of the Mammoth 



Hot Springs, Yellowstone Park 36 



Plate 5. 



A. Superficial erosion by water on clay hills. 



La Jolla, California 40 



B. Bare areas due to the action of gravity, 



Cafion of the Yellowstone River, 

 Yellowstone Park 40 



C. Bare areas due to the action of ice, 



Yosemite Valley, California 40 



Plate 6. 



A. Local and fragmentary deposit in a 



young ravine, bad lands, Scott's 

 Bluff, Nebraska 46 



B. Sand-bars due to deposit in streams. 



North Platte River, Scott's Bluff, 

 Nebraska 46 



C. Silting up of the Soledad Estuary, La 



JoUa, California 46 



Plate 7. 



A. Terminal moraine of the Nisqually 



Glacier, Mount Rainier, Washington; 

 bare area due to deposit by a glacier . 48 



B. Talus slopes of Scott's Bluff, Nebraska; 



bare areas due to gravity 48 



Plate 8. 



A. Roaring Mountain, Yellowstone Park; 



bare area due to steam and hot water. 50 



B. Mammoth Paint Pots, Yellowstone Park; 



bare area due to mud volcanoes .... 50 

 Plate 9. 



A. Salton Sea, California; portion of the 



bed exposed by evaporation 56 



B. Medanos Spit, San Diego, California; 



the tops of the dunes are gray with 

 Mesembryanthemum killed by frost . . 56 



PAOE. 



Plate 9 — Continued. 

 C. Wind-throw in pine forest. Leech Lake, 

 Minnesota 



56 



Plate 10. u j j 



A. Gravel ridges produced by a gold dredge, 



Chico, California ■ .• • 



B. Pond formed by a beaver-dam, Supenor 



National Forest, Minnesota • ■ o° 



C. Bare areas in Franseria-Abronia associes 



due to the destruction of the domi- 

 nants by Cuacuta salina, Medanos 

 Spit, San Diego, California 58 



PliATE 1 1 



A. Primary area colonized by mosses, ter- 



minal moraine of the Illecillewaet 

 Glacier, Glacier, British Columbia. . 60 



B. Secondary area colonized by SaUola, 



badlands, Scott's Bluff, Nebraska. 60 

 Plate 12. 



A. Snow-slide, Ouray, Colorado, showing 



primary rock area exposed on the 

 slope, and secondary area of dfebris 

 in the cafion 60 



B. Track of a snow-slide, Ouray, Colorado, 



marked by scrub 60 



Plate 13. 



A. Superficial wind erosion. Dune Point, La 



Jolla, California 62 



B. DeeiJ-seated water erosion, Torrey Pines, 



Del Mar, California 62 



Plate 14. 



A. Family of Pachylophus caespitoaus, 



Minnehaha, Colorado 64 



B. Colony of Dondia and Atriplex in a de- 



pression, the bed of a former salt 

 lake, Hazen, Nevada 64 



C. Tumbleweed, Salsola, on the Great 



Plains, Akron, Colorado 64 



Plate 15. 



A. Rootstock migration of Carex arenaria 



on dunes, Southport, England 66 



B. Mass of cone scales in mature forest of 



Pinus murrayana, Long's Peak, 

 Colorado 66 



C. Ready downward migration of trees and 



shrubs in Bear Creek Cafion, Colo- 

 rado Springs, Colorado 66 



Plate 16. 



A. Slow upward migration of herbs and 



shrubs, bad lands. Delta, Colorado . . 70 



B. Seeds, seedlings, and yearling of Pseudo- 



tsuga mucronata 70 



C. Seeds, seedling, yearUng, and 3-year old 



of Thuja plicata 70 



Plate 17. 



A. Ecesis in a primary area, summit of 



Pike's Peak, Colorado 72 



B. Ecesis in a secondary area denuded by 



hot water, Norris Geyser Basin, 

 Yellowstone Park 72 



