SECOND ANNUAL REPORT-STRATIGRAPHIC GEOLOGY. 
129 
localities, the contact between this formation and the overlying Pleisto¬ 
cene sand has been observed and it is everywhere marked by a distinct 
unconformity. The Pleistocene beds rest upon an undulating surface 
of the Nashua marl, which is clearly due to erosion, and the contrast 
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 alterna¬ 
tion 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 ex¬ 
tensive 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 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 Nashua marl is only 
imperfectly known, but it has been sufficiently studied to show that it 
resembles that of the Caloosahatchee marl. The most striking differ¬ 
ence 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 Ca¬ 
loosahatchee marl. This affinity with the fauna to the north suggests 
the existence of a cold current along the Atlantic coast which per¬ 
mitted a southward migration of the “Waccamaw” fauna. The lack of 
exposures in the south-central portion of the peninsula prevents the 
tracing of the connection between the two formations and the deter¬ 
mination of the limits of the southward migration of the species from 
the “Waccamaw” fauna. 
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