30 FLORIDA GEOLOGICAL SURVEY-I5TH 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 sel¬ 
dom 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 thirty- 
two feet. 
“Physiographic Expression: —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 Nlashua 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 Caloosahatchee marl. 
This affinity with the fauna to the north suggests the existence of a cold 
current along the Atlantic coast which permitted a southward migra¬ 
tion of the ‘Waccamaw’ fauna. The lack of exposures in the south- 
central portion of the peninsula prevents the tracing the connection 
