42 PROCEEDINGS: BOSTON SOCIETY NATri{AI> HISTORY. 
as Ammoph'da hrcmligulaia Fernald, Latfiyru.s iiKiritiiNu.f (L.) Bigel., 
Solidago scmpcrvirens L., and Aster novi-hdgii h., which are ubi- 
quitous on all the drier parts of the island ; there are also such species 
as Copfis tnfolia (L.) Salish., Pyrus arbutifoHa (L.) L. f., var. atro- 
purpurea (liritton) llobinson, Vaccinimn pcnnsykanicum Lam., Trl- 
entalis borealis Raf., MitcheUa repens L., Lmiicera caerulea L., var. 
cahescens Fernald & Wiegand, Linnaca 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 Poly podium vuUjarc L., a surpris- 
ing plant to find on a sand-dune island. Yet we learn from Warming' 
that in northern Europe it occurs on the gray sand dunes, and Fern- 
ald & 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' 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). 
^ Dawson, Sir John William: Acadian Geology, ed. 3, 37 (1878). 
