42 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 



as Ammophila breviligulata Fernald, Lathyrus maritimus (L.) Bigel., 

 Solidago sempervirens L., and Aster novi-belgii L., which are ubi- 

 quitous on all the drier parts of the island ; there are also such species 

 as Coptis trifolia (L.) Salisb., Pyrus arbutifolia (L.) L. f., var. atro- 

 purpurea (Britton) Robinson, Vaccinium pennsyhanicum Lam., Tri- 

 entalis borealis Raf., Mitchella repens L., Lonicera caerulea L., var. 

 calvescens Fernald & Wiegand, Linnaea borealis L., var. americana 

 (Forbes) Rehder, and Viburnum cassinoides L. These stretches here 

 called Empetrum Heaths are what J. Macoun in his article called the 

 " old land. " In this area he found Polypodium vulgare L., a surpris- 

 ing plant to find on a sand-dune island. Yet we learn from Warming 1 

 that in northern Europe it occurs on the gray sand dunes, and Fern- 

 aid & Long found it in 1919 on sheltered wooded slopes of sand hills 

 at Provincetown on Cape Cod. 



DUNE HOLLOWS The shallow hollows between the dunes are 

 often dry and destitute of vegetation, but if the hollows are deep, 

 they approach the water table which is relatively high. 



This water table has frequently been commented upon; for it is 

 well known that clear fresh water can be obtained by digging a few inches 

 or feet in any of the dune hollows. The level of this water table has, 

 of course, a relation to the height of the water in the fresh-water 

 ponds. But through all this is a fundamental factor which we can- 

 not yet explain. There is no evidence to show that there is any hard 

 or impervious stratum underlying Sable Island. If such a layer ex- 

 isted near the surface it would surely be known, and it would have 

 to be near the surface to govern the relative position of the water 

 table as observed. To the best of the writer's knowledge, no deep 

 borings have ever been made on the island. In discussing this ob- 

 scure feature of Sable Island, Sir J. W. Dawson 2 says, " Pools of fresh 

 water, however, appear in places, which would seem to imply that 

 there is an impervious subsoil. This may, however, be caused by the 

 floating of rain water on water-soaked sand, an appearance which 

 may sometimes be observed on ordinary sand beaches, where, in con- 

 sequence of their resting on the surface of the sea-water, these pools 

 or springs sometimes rise and fall with the tide. I am not aware, 

 however, that this occurs at Sable Island." Any such tidal vari- 

 ation in the level of the fresh-water ponds would be very conspicuous, 

 but no such feature has ever been observed on the island. We must 



1 Warming , Eugene: Oecology of Plants. English ed. 267 (1909). 



2 Dawson, Sir John William: Acadian Geology, ed. 3, 37 (1878). 



