abundant and characteristic are small foraminifera of the genus Orbitoides. From the predominance of these small fossils the formation has come to be known commonly as the Orbitoides Limestone. The formation contains in places large masses of flint. These flint masses seem to have been formed by replacement of calcium carbonate by silica carried in solution by the underground water, which circulates freely through the limestone. Locally, this originally porous and fossiliferous limestone has become compact and more or less perfectly crystallized. Apparently this change is also to be attributed to the effect of underground water. The Vicksburg Limestone doubtless underlies the entire State. It is a part of an extensive formation which encircles the Gulf of Mexico from Florida to Louisiana. In Alabama it makes up apparently the middle part of the St. Stephens or White Limestone, and has there, according to Smith, an estimated thickness of between two and three hundred feet.1 In Mississippi, Casey recognizes two faunal horizons in the Vicksburg Bluffs2, the upper of which contains Orbitoides as a characteristic fossil. Upon this basis Dall has proposed tentatively for the Orbitoidal phase of this extensive formation the term "Peninsular Limestone", from its typical occurrence in the peninsula of Florida.3

In Florida this limemstone lies at the surface in limited areas but is, for the most part, buried beneath later deposits. Good exposures are seen in the central portion of Alachua and in the southern part of Columbia Coun

1Report on the Geology of the Coastal Plains of Ala., Geological Survey of Ala. Eugene Allen Smith, State Geologist. 1894, pp. 107122. The Underground Water Resources of Ala. Eugene Allen Smith, Geological Survey of Ala. 1907. The Ala. Survey has not found it practicable, however, to separate any part of the White Limestone as it occurs in that State from the Eocene. (Coastal Plains, p. 109.)

2 Proceedings Academy Natural Science of Philadelphia, pp. 513-518, 1901.

3Trans. Wagner Free Institute Sci. Vol. III, pt. VI, p. 1554, 1903.

ties. It is exposed locally throughout an area extending from Pasco County to South Columbia County and locally west to the Suwannee River. The largest exposed areas lie in Pasco, Hernando, Marion and Levy Counties. Lying upon the Orbitoidal limestone and probably conformable with it is a thin limestone of similar character known as the Ocala Limestone from its typical exposure at the Meffert lime kiln at Ocala. These two formations make up the Lower Oligocene of Florida.

The Upper Oligocene formation consists of limestones and clays. Over much of the north central and western part of the State, these deposits lie at or near the surface, forming a thin coating which rests unconformably upon an eroded surface of the older limestone. The Suwannee River cuts across them between Hamilton, Columbia and Suwannee Counties. They are also cut by the Apalachicola River from Chattahoochee to Bristol. South of the Orbitoidal limestone area these late Oligocene formations crop out along the Hillsboro River, Tampa Bay and elsewhere. They doubtless also extend to the east in that direction underlying later formations.

The Miocene deposits, next above, lie along the east side of the peninsula from Jacksonville to Lake Worth. Deposits representing the same time interval occur in west Florida from Tallahassee to Pensacola, lying between the Oligocene and the coast. Marine Pliocene deposits, consisting of marls and shell beds, occur over much of the southern end of the peninsula, being best exposed along the Caloosahatchee River. Residual and river-formed Pleistocene deposits are to be expected locally throughout the State. A Marine Pleistocene shell rock occurs along North Creek, near Osprey. Similar deposits have been reported from other localities. The Miami Oolite limestone is apparently the most extensive marine Pleistocene deposit in the State. This Oolitic limestone is known to reach north to or beyond Ft. Lauderdale, forming the eastern boundary of the Everglades and dipping to the west. Miami, New River, and other

streams from the 'glades cut across it.

Its present altitude is due to a mild elevation of the east coast which occurred probably during or at the close of Pleistocene time.

The recent formations in the State include rock accumulations of several varieties. Loose sands are not infrequently firmly cemented by the iron deposited from chalybeate springs. A rock so formed, although comparatively recent, may nevertheless be extremely hard. An example of such rock containing numerous snails is found along Sarasota Bay. Marl deposits have been observed to accumulate at the point of meeting of fresh and salt water. Coquina rock forms as a result of the more or less complete cementation of masses of shells. Sand dunes occur along both the east and the west coasts, while shell mounds and Indian remains are found in many places.

FOSSILS CONTAINED IN THE FLORIDA FORMATIONS.

*

The fossil record contained in the rocks of Florida is above the average in completeness. This is especially true of the marine invertebrate fauna. From the Oligocene period to the present time there is an almost unbroken series of rock formations made up largely of the remains of such marine invertebrates as lived during the time of the formation of these rocks. W. H. Dall says:* "The State of Florida presents the most complete succession of Tertiary and post-Tertiary fossil-bearing strata of any part of the United States. Nowhere else can the problems of descent with modifications during Cenozoic and later time be so well studied in the fossil and recent faunas." More than fifteen hundred species of invertebrates have been recognized in the Florida formations, and it is probable that a much larger number actually occur. As early as the late Oligocene a few living species of marine invertebrate appear. The proportion of modern species in the fauna increases with each period from that time to the present.

*Bull. U. S. Geol. Survey No. 84, p. 85, 1892.