186 PROCEEDINGS OF 



Many specimens of Arcii idonca can bo easily obtained here, witli connected 

 valves, in the stratum of clay ; but cxccptinjj the Panoptna, 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.boach 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, wo observe, occasionally, a valve of an undetermined Ostrea, 

 an estuary shell. One of the most abundant univalves is Buccinum trlvittatum, 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 JV. 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 siles, 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 nmeh 

 greater thickness, and the shells are more friable ; the cliff also rises to a greater 

 elevation. Here the beautiful fossil Artemis acctahulum, is particularly abundant. 

 To the south of this, near Windmill Point, Fusus quadricostatus, of Say, is moro 

 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 acetahiilum, Fusus parilis, F. quadri- 

 costatus, and Voluta mutabilis. The east bank of the river presents a cliff of 

 nearly the same elevation, fifleen 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 solenitc, many of \vliich are 

 twelve inches in diameter, and profusely imbedded in clay near the level of the 

 beach. Near this locality we remained several days, under the hospitable roof of 

 our cxccllcut friend Dr. James W. Roach. 



Organic Remains found on St. Mary's River, 

 Univalves. Univalves. 



ActiEOii ovoidcs, Conrad. Natica heros, Say. 



Bulla acuminata, Sowerby. Nalica diipliratu, Say. 



Buccinum trivillalum, Say. Plcurotoma bicatenaria, Conrad. 



Buccinum lunatum. Say. Plcurotoma limatula, Conrad. 



Buccinum quadratum, Conrad. Plcurotoma commuuis, Courad. 



