332 



George E. Nichols, 



buried by the sand, but at the present time trees are scarce and 

 of merely sporadic occurrence. 



The South Bay spit with its dunes (Fig. 31), from the stand- 

 point of physiographic ecology, affords in itself a study of 

 exceptional interest, and has already been written up in some 



detail by Dr. Harvey ('18). 

 In crossing the spit from 

 the seaward margin on the 

 east to the "pond," which is 

 between one and two miles 

 wide, one encounters in order 

 (i) the lower beach, (2) 

 the middle beach, (5) the 

 upper beach, and (4) the 

 salt meadows and marshes 

 which border the spit on its 

 western side. Along the sea- 

 ward edge of the broad 

 upper beach is a row, some- 

 times double but mainly 

 single, of sand-dunes, mostly 

 less than six feet in height, 

 but in one locality rising to 

 fully fifteen feet. Some at 

 least of the dunes have 

 originated in moist depres- 

 sions, or "pans," in which 

 grow Juncus balticus littoralis 

 and Iris versicolor. On many 

 of the lower dunes, as might 

 be expected, the sand-reed 

 (Ammophila) is the pre- 

 dominant plant, fulfilling in 

 connection with dune-formation the twofold function of (i) 

 breaking the force of the wind and causing it to drop part of its 

 burden of sand, and (2) binding together and holding, by means 

 of its copious, slender roots, the sand which thus accumulates. 

 More often than not, however (Fig. 32), the sand-reed is absent 

 and in its place occurs a luxuriant growth of wire-grass (Poa 

 compressa) , which seems fully competent to carry out the 

 functions elsewhere performed by the sand-reed. 



Figure 2,2. — Low dunes at South 

 Pond, Aspy Bay ; in foreground, 

 Poa compressa acting as a sand- 

 binder. 



