A variety of lithostratigraphic units may be outlined within the pre-Cretaceous crystalline basement of the Atlantic and Gulf Coastal Plains. An expanse of undeformed granite occurs within central peninsular Florida; biotite within the pluton yields 40 Ar/ 39 Ar plateau dates of ca. 525 to 530 Ma. The high-level character of the granite and its emplacement age are similar to post-kinematic granitic plutons within northern portions of the Rokelide orogen in Guinea, West Africa. A sequence of calc-alkaline, felsic volcanic-volcaniclastic rocks, together with associated hypabyssal granite, occurs throughout the basement terrane. These are variably altered and display markedly discordant 40 Ar/ 39 Ar age spectra. Crystallization ages are likely best represented by ca. 675 to 690 Ma Rb-Sr whole-rock and 40 Ar/ 39 Ar hornblende plateau ages previously reported for correlative calc-alkaline granites exposed in southeastern Senegal. A Lower Ordovician–Devonian sedimentary sequence with non-Laurentian paleontological characteristics occurs within the Suwannee basin of the northern Florida subsurface. Detrital muscovite from Lower Ordovician sandstones in the succession records 40 Ar/ 39 Ar plateau ages of ca. 500 to 510 Ma. The sequence is similar to that within the Bové basin in Senegal and Guinea. A small area of high-grade metamorphic rocks occurs in the east-central Florida subsurface. Hornblende from this terrane records 40 Ar/ 39 Ar plateau ages of ca. 485 to 495 Ma. The character and post-metamorphic cooling history of these rocks are similar to that of units within the Rokelide orogen in Sierra Leone and Liberia, West Africa. In the subsurface Wiggins Arch of southwestern Mississippi, hornblende and biotite from interlayered gneiss and amphibolite record similar 40 Ar/ 39 Ar plateau ages of ca. 300 to 310 Ma. Phyllite from a lower-grade metasedimentary sequence penetrated in the Wiggins Arch of southwestern Alabama records a 40 Ar/ 39 Ar whole-rock plateau age of ca. 315 Ma. Characteristics of the pre-Cretaceous basement units suggest that they represent an extension of the Mauritanide, Bassaride, and Rokelide orogens of West Africa. There is no apparent record of Paleozoic tectonothermal activity in central and southern portions of the Atlantic and Gulf Coastal Plain subsurface basement terrane. This is in marked contrast to complete late Paleozoic reworking of basement units penetrated in the area of the Wiggins Arch. This suggests that a major dextral transcurrent fault system was likely active during the late Paleozoic, and that proximal basement units were directly involved in collisional aspects of Pangea assembly. The various units of the Atlantic and Gulf Coastal Plain basement are not correlative with any of the northern non-Laurentian terranes exposed in the southern Appalachian orogen (e.g., Carolina terrane of the eastern Piedmont) which had earlier accreted to exterior positions along the eastern margin of the North American craton. These were transported into their present structural positions along a basal décollement during late Paleozoic collision of Gondwana and Laurentia, and are separated from the stranded Gondwana units of the Coastal Plain basement by a suture approximately marked by the Brunswick-Altamaha magnetic anomaly.

Abstract Paleozoic rocks exposed in the Appalachian Mountains are bordered on the east and south by the Atlantic and Gulf Coastal Plains, and rocks of the Paleozoic orogenic belt may be traced beneath the cover of post-orogenic Mesozoic-Cenozoic Coastal Plain strata (Plate 6). Large-scale lithotectonic components of the exposed Appalachian orogen include the foreland fold-thrust belt and internal metamorphic belts (collectively called the Appalachian Piedmont), which locally contain internal basement massifs. External basement massifs and discontinuous belts of low-grade metamorphic rocks are distributed along the boundary between the fold-thrust belt and the Piedmont. Accreted terranes are identified in the internal metamorphic belts.

L ittle has been published concerning the fossil Crustacea of eastern and southern United States. The United States Geological Survey and the United States National Museum have been gradually accumulating specimens, but the sum total is moderate. Crustacean remains, compared to molluscan, are scarce. The shells are thin, fragile, and easily destroyed, so that the remains consist largely of chelae or parts of chelae, as these are usually thicker than the carapace and other appendages. The number of species at hand is relatively small; more are known from the lower Cretaceous of Texas and the Midway of Alabama than elsewhere. In the Cretaceous the predominating genera of shrimp-like forms are Hophparia and Callianassa-, the former belongs to the family, Homaridae, best known from the common lobster; the latter is a burrowing shrimp of a type which persists at the present day to a limited extent but which in ancient times was noted for the great number of species and individuals. The largest crustacean here recorded occurs in the Comanche series of Texas, a Palaeastacus figured on Plates 3–5. Several species of the genus Linuparus of the family Palinuridae indicate the derivation of Recent L. trigonus of Japan. The three pagurids, or hermit crabs, are referred to genera now living. A prevailing genus of true crabs is Necrocarcinus, a Calappid which became extinct after the Eocene. Fairly abundant are the Gymnopleura or Raninidae, representatives of which still persist in the waters bordering the Coastal Plain. Notable is the presence of two isopods, Aegidae, rare among fossils.

Abstract The Atlantic and eastern Gulf Coastal Plain (Fig. 3; Table 2, Heath, this volume) is a gently rolling to flat region of about 400,000 km2 extending from Long Island, New York, to eastern Mississippi. It is underlain by a wedge of unconsolidated to semiconsolidated, predominantly clastic sedimentary rocks that range in age from Jurassic to Holocene. The rocks consist mostly of sand, silt, and clay, but also contain lesser amounts of gravel and limestone. They thicken seaward from a feather edge at their updip limit, where they overlie older metamorphic, igneous, and consolidated sedimentary rocks of the Piedmont and other physiographic provinces, to 3,000 m in eastern North Carolina and 6,400 m in southern Alabama, thickening further beneath the Atlantic Ocean and Gulf of Mexico.