186 
PROCEEDINGS OF 
Many specimens of Area idonea can be easily obtained here, with connected 
valves, in the stratum of clay ; but excepting the Panopaea, the other large bivalves 
generally occur disunited. I have, however, occasionally found a whole Mactra 
ponderosa, Venus tetrica, V. alveata, Artemis acetabulum, and great abundance of 
the small Corbula cuneata. Fragments of shells, comminuted by attrition in the 
surf, occur plentifully in this deposit; which circumstance, in connection with the 
prevalence of single valves, shows that the deposition took place near enough to the 
ancient sea-beach to be influenced by the currents along the shore, or perhaps by 
the undercurrent of the surf, during the prevalence of violent tempests. In further 
confirmation of this, we observe, occasionally, a valve of an undetermined Ostrea, 
an estuary shell. One of the most abundant univalves is Buccinum trivittatum, a 
recent species of the eastern and middle Atlantic coast; and its usual associate in 
the present sea, Buccinum lunatum , is very common. Natica heros, and N. dupli- 
cata, (Say,) two recent univalves, with a similar geographical range, are of frequent 
occurrence in the clay. Some of the large univalves are most common in the are¬ 
naceous stratum, but none are limited to it. Occasionally, masses are found along 
the shore, which have been indurated by silex, originally in a gelatinous state, the 
surfaces studded by shells of various species. These siliceous beds, no doubt, are 
owing to the infusoria which existed in this tertiary period. North of Porto Bello, 
the residence of the Rev. Mr. Mitchell, the arenaceous stratum becomes of much 
greater thickness, and the shells are more friable ; the cliff also rises to a greater 
elevation. Here the beautiful fossil Artemis acetabulum, is particularly abundant. 
To the south of this, near Windmill Point, Fusus quadricostatus, of Say, is mor8 
numerous and perfect than in any other known locality of the formation. The 
beach, for nearly a mile, is strewed with fine fossil shells of the large bivalves and 
univalves, in great perfection, among which the most conspicuous are, Mactra pon¬ 
derosa, Venus tetrica, ,V. Mortoni, Artemis acetabulum , Fusus parilis, F. quadri¬ 
costatus, and Voluta mutabilis. The east bank of the river presents a cliff of 
nearly the same elevation, fifteen or twenty feet. The clay rises about three feet 
above the level of the water, containing the same group of shells, largely mixed 
with fragments, which prevails on the opposite shore. The top of the arenaceous 
stratum is here become a hard ferruginous rock. Near the southern termination of 
the cliff, towards the mouth of St. Inigoe’s creek, the fossils are no longer visible, 
except in indistinct impressions, the material of the shells having been converted, 
in nature’s grand laboratory, into splendid masses of selenite, many of which are 
twelve inches in diameter, and profusely imbedded in clay near the ldvel of the 
beach. Near this locality we remained several days, under the hospitable roof of 
our excellent friend Di*. James W, Roach. 
Organic Remains found on St. Mary's River. 
Univalves. 
Actaeon ovoides, Conrad. 
Bulla acuminata, Sowerby. 
Buccinum trivittatum , Say. 
Buccinum lunatum , Say. 
Buccinum quadratum , Conrad. 
Univalves. 
Natica heros, Say. 
Natica duplicata, Say. 
Pleurotoma bicatenaria, Conrad, 
Pleurotoma limatula, Coni’ad. 
Pleurotoma communis, Conrad, 
