MICROSCOPICAL OBSERVATIONS. j.g 



TAMPA. — continued. 



On the beach in front of the flagstaff at Fort Brooke, I collected the follow- 

 ing: 



DlATOMAOE^. 



Alg^. *Achnanthes ? arenicola, B, see page 38. 



Sargassum vulgare, Ag. ' Bacillaria paradoxa, Elir. 



Spyridia filamentosa, Harv. Grammatophora stricta, Ehr. 



Ceraniium clavulatum, Ag. Gallionella sulcata, Ehr. 



Rhabdonema adriaticum, Kg. 



On the west side of the bay, the following Alga; were found on the beach at 

 low tide, viz : 



Bangia fusco-purpurea, Lyngb. Gracilaria multipartita, J. Ag. 



Calothrix confervicola, Ag. Polysiphonia Olneyi ? Harv. 



Ceramium clavulatum, Ag. 



INFUSORIAL STRATUM NEAR TAMPA. 



Between the ferry at Tampa and the well known locality of silicified corals 

 at Ballast Point, on Hillsborough Bay, and directly on the shore of the bay, I 

 detected a highly interesting stratum of fossil marine Diatomacese or Infusoria. 

 It is exposed for at least a quarter of a mile along the shore, and from five to 

 ten feet of its thickness may be seen. In its external characters, (whiteness, 

 lightness, fissility, &c.,) it has some resemblance to the infusorial strata of Vir- 

 ginia, but is much more indurated, so that, although it is easy to show that it is 

 made up of the remains of Diatomaceae, spicules of sponges, &c., it is yet diffi- 

 cult to isolate and determine the individual species. The following forms, how 

 ever, were distinctly recognized, viz : 



Aetinoptychus senarius, Ehr. GalHonella sulcata, Ehr. 



Coscinodisci, undetermined fragments. Rhaphoneis rhombus, Ehr. 



Denticella ? tridentata, Ehr.^Zygoceros Tuomeyi, B. 



with numerous sponge spicules. 



This infusorial earth, like that at Petersburg, Va., changes in a singular man- 

 ner, to a salmon color, when exposed to the vapor of Tui'pentine or Canada Bal- 

 sam. The geological position is probably in the upper part of the Eocene Ter- 

 tiary, for a bed of shells, which apparently belong to that epoch, lies a short dis- 

 tance to the east of the infusoi'ial bed. 



This discovery of a marine infusorial stratum, similar to those of Virginia and 

 Maryland, but at so great a distance from them, is, I think, of much interest, 

 and gives reason to hope for the detection of similar deposits at many interme- 

 diate points. 



Some interesting remarks on the geology of the localities in the vicinity of 

 Tampa and Ballast Point, by J. H. Allen, may be found in Silliman's Journal, 

 New Series, Vol. I., p. 38, and others by T. A. Conrad, in the same series. Vol. IL, 

 pp. 36, 399. 



