240 H. D. HOUSE 



dunes, indicating the former level of the ground before the invasion 

 of the dunes. At a former time the forests were apparently 

 much more extensive here, perhaps during a period of greater 

 humidity than the present, when the movement of the sand was 

 reduced to a minimum and the forests had a chance to invade 

 much of this sandy region. This is probably the case because 

 dune sand in the form of hilly ridges is common much farther 

 inland than the sand dunes now extend, and is covered by 

 forests in character similar to those still remaining within the 

 dune area, viz: Douglas fir, Sitka spruce. Shore pine, Port Orford 

 cedar, etc. Nor has the lumbering operations on these inland 

 dune areas caused any renewal of activity on the part of the sand, 

 although it has had considerable effect upon the character of the 

 second growth as compared with the second growth conditions 

 farther inland on clay soils. 



Thus one can imagine that this natural phenomenon works in 

 cycles corresponding with the climate and that the present ad- 

 vance of the sand over the forests indicates a gradual decrease in 

 the humidity of the climate within the past century, although 

 some of the trees on the dune sand are easily over two hundred 

 years of age. Certainly the hand of the lumberman has had little 

 if anj^thing to do wdth the advance of the sand here, for the forest 

 on the dunes proper are too scattering and too poor, compared 

 with others in this region, to tempt the lumberman, and have 

 never been touched. Another possibility in this connection is 

 that the force of the prevailing winds may have varied periodically. 



The greatest height is attained by the dunes at a distance of 

 three or four miles inland, where the advance of the dunes is 

 checked by the accumulating height of the sand and by the north 

 branches of Coos Bay, which lie here between the dunes and the 

 mainland. Higher dunes, however, of a former period lie farther 

 inland on the mainland side of the north and south branches of 

 the bay but are now covered by forests or by second growth. 



The undergrowth of the forests on the sand dunes is even more 

 impenetrable than that on the mainland, consisting of a larger 

 percent of the more rigid species of shrubs, such as Manzanita 

 (A/'ctosiaphylos tomentosa), Ocean spray {Schizonotus ariaefolius) , 



