Five belts of metamorphosed sedimentary and volcanic rocks underlie southwestern Maine and southeastern New Hampshire: Middle Ordovician Falmouth-Brunswick sequence; Middle and Late Ordovician Casco Bay Group, and Late Ordovician to Early Silurian rocks of the Merribuckfred Basin; Late Ordovician to Early Silurian rocks of the East Harpswell Group; Silurian to Early Devonian rocks of the Central Maine Basin; and highly tectonized enigmatic rocks of the Rye complex of uncertain age. Stratigraphic reassessment and new U/Pb zircon ages support a model of east-directed Middle Ordovician subduction beneath Miramichi, a peri-Gondwanan block, and formation of the Falmouth-Brunswick–Casco Bay volcanic arc complex that is roughly correlative with arc activity on strike in New Brunswick. Passive Late Ordovician sedimentation in a reducing restricted backarc basin followed. Late Ordovician to Early Silurian volcanic rocks and volcanogenic sediments (East Harpswell Group) support west-directed subduction under the Miramichi block. Late Ordovician to Early Silurian turbidites accumulated in the Merribuckfred Basin between the Falmouth-Brunswick–Casco Bay arc and Ganderia to the east. The collision of Ganderia with the Falmouth Brunswick arc in Late Silurian time represents an early phase of the Acadian orogeny, during which the Merribuckfred rocks were deformed, metamorphosed, intruded, and uplifted. Simultaneously and inboard, the Central Maine Basin received sediment eroded mostly from Laurentia. Later, during the Late Silurian and Early Devonian, uplifted Merribuckfred basin rocks became the major source of sediments for the Central Maine Basin. A later phase of the Acadian orogeny resulted in Middle Devonian deformation, metamorphism, and intrusion of rocks of all six belts.

This paper is a case history of coastal development at Camp Ellis, Saco, Maine. It begins in 1867 with dredging and jetty construction at the mouth of the Saco River to facilitate commercial navigation. Beach accretion, resulting from tidal delta collapse, was followed by residential development before the ephemeral nature of the shoreline was recognized. A misunderstanding of the riverine source of beach sand and the net, northward direction of longshore transport confounded U.S. Army Corps of Engineers (USACOE) efforts to maintain navigation and the adjacent beach. Beach erosion at Camp Ellis claimed dozens of properties before the role of the north jetty at the mouth of the Saco River became apparent to state and university scientists. Erosion also led to sand migration to the north and to the closure of the Little River inlet and growth of Pine Point spit. This spit was later developed and a jetty was placed at its tip to preclude continued accretion into the Scarborough River inlet. Despite numerous studies, the USACOE failed to recognize the connection between beach erosion at Camp Ellis and beach accretion at Pine Point. Under political pressure, the USACOE recently conducted detailed modeling studies and has proposed construction of breakwaters seaward of Camp Ellis to solve the problem. A discussion of the pros and cons of this proposal is presented in light of the long history of development at Camp Ellis.