30 FLORIDA GEOLOGICAL SURVEY-15TH ANNUAL REPORT

between the fossiliferous marl and the overlying barren sands helps to emphasize the break between the two.

 "Lithologic Character:-The Nashua marl bears a strong lithologic resemblance to the Caloosahatchee marl. There is the 'Same alternation of sand beds with shell marl. The matrix of the Nashua marl, while usually calcareous, is always more or less sandy and sometimes consists of nearly pure'sand. The shells are commonly well preserved though locally a marl consisting of broken and eroded fragments of shells is not uncommon. However, the organic remains are so well preserved that it is easy to obtain good collections of fossils from this formation.
 "Thickness:-The Nashua marl is much thinner than the Miocene strata. This fact, together with its distribution beneath the lowlands near the coast, indicates that the Pliocene submergence was less extensive than the Miocene; and the presence of shallow-water fossils shows that the Pliocene sea did not attain any great depth over that part of the State where the marine beds are now exposed. The Nashua marl is seldom more than six or eight feet thick, but locally it attains a greater thickness. A series of samples of sand and marl from a well at DeLand indicates that at that locality this marl has a thickness of about thirtytwo feet.
 "Physiographic LExpressio:-The *Nashua marl occupies the St. Johns Valley, where it underlies a broad terrace bordering the stream. It probably occurs beneath the plain east of St. Johns River, but the overlying Pleistocene forms such a thick mantle that the Nashua marl has no influence on the topography. On the whole, this formation has little or no influence on the topography of the State.

 "Paleontologic Character:-The fauna of the Niashua marl is only imperfectly known, but it has been sufficiently studied to show that it resembles that of the Caloosahatchee marl. The most striking difference between the faunas of the two formations is the existence of certain species in the Nashua marl which occur in the 'Waccamaw' fauna of the Carolinas, but are not known to be present in the Caloosaatchee marl. This affinity with the fauna to the north suggests the existence of a cold current along the Atlantic coast which permitted a southward migration of the 'Waccamaw' fauna. The lack of exposures in the southcentral portion of the peninsula prevents the tracing the connection