380 Part IV. Chapter 2. 
sagittata var. ovata, Polygala polygama, Trifolium arvense, Tephrosia (Cracca) 
virginiana, Prunus maritima, Chrysopsis falcata, Diplopappus (Doellingeria) 
lineariifolius, Arctostaphylos uva-ursi; Kalmia angustifolia, Asclepias obtusi- 
folia, Salix tristis, Cypripedium acaule, Pinus rigida. The bulk of the 
underbrush consists of Rhus copallina, Pyrus (Aronia) arbutifolia, Amelanchier 
canadensis, Viburnum dentatum, Myrica carolinensis, Myrica gale, Rhododendron 
(Azalea) viscosum, Andromeda ligustrina, Gaylussacia frondosa, G. resinosa, 
Vaccinium corymbosum, V. vacillans, V. pennsylvanicum, while on the ground 
are Epigaea repens, Gaultheria procumbens, Trientalis americana and Potentilla 
argentea‘). Some of these plants form a pine barren element stronger than 
in Nantucket and must be considered as northeastward migrating plants. 
(Sand Barren Formation). 
At present, the island of Nantucket is practically treeless, but there is 
abundant historic evidence that this island when first settled was generally 
forest clad and that the trees of oak and pine were sufficiently large to afford 
ship-timber. Nevertheless the flora of Nantucket is extremely rich and varied. 
A peculiar feature is the presence of Opuntia vulgaris and O. Rafınesqui in 
the region north of Coatue Sound about Great Head. Ouereus iicifolia ass0- 
ciated with Zpigaea repens is still abundant in the scrub form on the commons 
and with several other plants represents the northeastern extension of the 
pine barrens, 
Corema Conradii, Arctostaphylos uva-ursi, Hudsonia ericoides, H. tomentosa occur on the 
plains of Nantucket, but Calluna vulgaris and Erica cinerea, E. tetralix are striking 
elements in the flora. 
In some swamps a few trees are found: Ouercus alba and rubra, Hicoria 
alba, Fagus, Nyssa, Ilex opaca. 
The flora of Block Island may be divided into that of the hills, the peat 
bogs and pond holes, the salt marshes, the sand dunes and the salt water, 
the latter being exclusively algal, except for Zostera. W. W. BAILEY and 
J. F. CoLLins list 294 species of the flowering plants and ferns found by them 
on the island. The island is ‚practically treeless and hence devoid of such 
vegetation as is depend upon growth under a forest cover. But there is abun- 
dant evidence that a tree flora formerly existed, consisting of pine, oak, beech, 
hickory. Block Island lacks the plain flora of southern affinity found on Long 
Island, Martha’s Vineyard and Nantucket. This is explained by reference to 
the past geologic history of the island. At the close of the ice age, there 
was a continuous strip of land, in fact the seaward extension of the great ter- 
minal moraine, separable into two portions an elevated northern border and 
a southern plain representing what remained of the old Tertiary coastal plain. 
Since the glacial period, Block Island has lost all of its plain region and the 
accompanying flora, and is now merely an isolated portion of the terminal 
1) HoLLick, ARTHUR: Observations on the Geology and Botany of Martha’s Vineyard. 
Transactions New York Academy of Sciences 1893—94 XII: 17—2ı 
