PHYSICAL CONDITIONS INDICATED BY THE FLORA OF THE CALVKltT IdRMATlOX. 



65 



Among the recent species with which the 

 Calvert forms arc compared three range as 

 far north as soutliern Canada and one other 

 ranges into New Enghvnd. On the other 

 hand, all the forms, inidnding the fonr jnst 

 mentioned, range southward to Florida or 

 Texas and five of these extend into the Ameri- 

 can Tropics. It is obvious that these wide- 

 ranging forms are of slight value hi an en- 

 deavor to estimate the climatic conditions 

 along the coast in Calvert time. More sig- 

 nificance attach(>s to the northern limits of 

 the other existing forms with which those of 

 the Calvert arc compared. Three of these 

 have their northern limits in southern Ari- 

 zona and New Mexico, two in Georgia, two 

 in North Carolina, four in Virginia, one in 

 Maryland, and two in Delaware. Some of the 

 comparisons with recent forms are closer or 

 more significant than others. Among thes(> 

 may be cited those with Taxodiurn distichum, 

 Quercus chapmani, Planera aqiiafica, Berclumia 

 scandens, and Pieris niiida. Of these, tlie bald 

 cypress (Taxodiurn distichum) reaches its north- 

 ern limit in soutliern Delaware; Quercus chaji- 

 rnani is confined to the coast of Georgia and 

 the Gulf of Mexico ; Planera reaches northward 

 to the Coastal Plain of North Carolina; and 

 Berchcmia and Pieris extend to the Coastal 

 Plain of Virginia. It is obvious that if these 

 comparisons arc legitimate the Calvert flora 

 would find its most favoral)le conditions for 

 existence along the present south Atlantic 

 and Gulf coasts. 



Another method of approach is furnished by 

 comparing the Calvert flora with the contem- 

 poraneous floras of Europe. Of the 26 Cal- 

 vert species, 7 are identical with and 10 are 

 extremely (dose to forms of the Tortonian of 

 Europe. The Tortonian has a very extensive 

 flora, and as a result of the elaborate analysis 

 by Ileer it was considered to indicate a mean 

 annual temperature of 6.5°. 



Regarding the specific environment of the 

 difTerent Calvert species, I consider the follow- 

 ing as denizens of river or estuary swamps: 



Fraxinus richmondensis. 

 Finns sp. 



Salvinia I'ormosa. 

 Taxodiurn duhium. 

 Nyssa gracili.s. 



Tlie following may be considered as dwellei 

 on river bars or behind coastal sand dunes: 



Salix raeana. 

 Ulmus basirordata. 

 Cassia torafonuis. 

 Keris scrobiculata. 



Platanus areroides. 

 Bercheinia priscaformis. 

 Carpinus grandis. 



Those which probably flourished in low l)ot- 

 toms, on the lower flood plains of streams, are 



Carpimi.'^ grandis. 

 Planer.i uiigeri. 

 Platanus aceroides. 

 Berchemia priscaformis. 



Most of these could readily live also in river 

 or estuarj- swamps. 



The species which may legitimately be con- 

 sidered to have been inhabitants of the strand 

 or of coastal dunes are 



Podogonium ^•irginianum. 

 I^eguiuinosite.s falvertensis. 

 Ficus richmondensis. 

 Pieris scrobiculata. 



Quercus calvertonensis. 

 Quercus Ichnianni. 

 Quercus chapniauilnlia. 

 Phyllites < ercocarpifolia. 

 Csesalpinia ovali folia. 

 Cassia toraformis. 



Dalbergia calvertensis. 

 Rhus milleri. 

 Ilex calvertensis. 

 Vaccinium cf. V. textum. 

 Celiistrus bruckmanni. 

 Pinus sp. 



AU but Salvinia and Cassia were probably 

 arborescent, and Cassia may have been. All 

 the dicotyledons except Fraxinus, Carpinus, 

 Platanus, Ficus, and Quercus calvertonensis 

 show marked reduction of the leaf lamina-, 

 clearly indicating a sandy habitat or a swamp 

 habitat, the latter being physiologically dry 

 and in its effects much like the former. 



The leaves of the oaks, Berchemia, Podogo- 

 nium, PhyUitcs cercocarpifolia, Dalbergia, Rhus, 

 Ilex, Vaccinium, and Celastrus are coriaceous 

 or subcoriaceous, and those of the Pieris are 

 tomentose, both features tending to prevent 

 transpiration and indicating a physiologically 

 dry habitat as well as exposure to abundant 

 sunshine. 



In comparing the two localities, that at 

 Richmond clcarlj- indicates a low coast which 

 was lined with cypress swamps and in which 

 the very inconsiderable run-off carried only 

 the finest muds. That in the District of Co- 

 lumbia, in its small-leafed oaks. Ilex, Vacci- 

 nium, Pieris, and abundance of Leguminosa^, 

 as clearly indicates a region of dunes compara- 

 ble with the present Santa Rosa Peninsula, be- 

 tween Pensacola Bay and the Gulf of Mexico. 



Physical conditions may produce decided 

 differences in the flora of the continental mar- 

 gin and the marine life of the sea which washes 

 it, as for example in the English Pliocene, where 

 the only avenue of immigration for terrestrial 

 plants and fresh-water mullusks was from the 

 south, while the onl}' avenue of immigration 

 for the marine fauna lay in the cool currents 

 that entered the North Sea from the north. 

 However, the Calvert fossils do not represent a 

 northward extension of tlie south Atlantic and 



