A Contribution to the Geologic History of the Floridian Plateau. 151 



water must have been comparatively quiet during the deposition of the Hmestone. 

 The incUision of a small percentage of land-derived sediments and in some places 

 of fresh-water shells shows that a portion of the limestones of Vicksburg age were 

 probably deposited at no great distance from land. Locally the calcareous sedi- 

 ments appear to have contained large quantities of silica, probably in the form of 

 tests of microscopic plants (diatoms) and spicules of sponges. (Florida Geol. Surv., 

 2d Ann. Report, p. 162, 1910.) 



The most persistently conspicuous fossils of this group of rocks are 

 foraminifera. Specimens and species of the genus Orbitoides are the 

 most abundant. This genus occurs not only from bottom to top, but 

 extends upward from the Jackson ' below, and into the higher Chatta- 

 hoochee. - 



In the Jackson at Montgomery, Lotiisiana, Orbitoides is associated 

 with shallow-water corals, as Astrangia; in the Vicksburg at Rosefield, 

 Louisiana, and in Mississippi and Alabama it is associated with shallow- 

 water moUusks, as Ostrea. The Vicksburg corals of Mississippi indicate 

 a depth of water not over 50 fathoms, and it may have been much shal- 

 lower. As the same species found in Louisiana, Alabama, and Mississippi 

 occur in Georgia, a similar moderate depth is inferred for that region. 

 The fauna of the area extending from Louisiana to the Savannah River 

 distinctly indicates shallow-water conditions, probably a maximum depth 

 of 50 fathoms, as the faunal associations of Orbitoides are those of 

 shallow water, or less than 100 fathoms. Doctor Dall has given a list 

 of species from the Ocala limestone in his Tertiary Fauna of Florida.'' 



The recent collections made by the Bureau of Fisheries steamer 

 Albatross in the Philippine Islands throw additional light on this problem. 

 At Station D 5179, off the northeast shore of Tablas Island (depth 37 

 fathoms, bottom temperature 76.2° F., bottom hard, sandy), hosts of 

 foraminifera were obtained, two of which were identified by Dr. J. A. 

 Cushman as Operculina coniplanata var. granulosa and Amphistegina 

 lessoni. The material is remarkably similar to that of which the Vicks- 

 burg limestones are composed ; and the two are faunally so similar that 

 it seems a sound opinion to consider the conditions of depth and tempera- 

 ture for the two deposits as similar.'' Operculina complanata var. granu- 

 losa is a common fossil in the Vicksburgian rocks in southern Georgia. 



Mr. A. H. Clark informs me that he found large numbers of an 

 OrbitolitesAi\ie form in shell sand brought up on the flukes of an anchor 

 on the Grenadine bank near Union Island in a depth of between 4 and 

 7 fathoms. 



The data presented in the foregoing remarks and the conclusion as 

 to the depth of the Vicksburg Sea mean that the Floridian Plateau 

 existed in Vicksburg time, and that its southern extent was about as 

 great as it is at present. The date of the origin of the Plateau is therefore 

 pre-Oligocene. 



' Orbitoides dispansa (Sow.) and O. papyracea (Boub^e) are found in the 

 Jackson at Montgomery, Louisiana. 



^ Orbitoides occurs in the basal Chattahoochee in the vicinity of Bainbridge, 

 Georgia. O. dispansa (Sowerby) is the usual species. 



' Wagner Free Institute. Transactions, vol. iii, part vi, 1903. 



* I am indebted to Dr. Paul Bartsch for the opportunity of using this note. 



