Metavolcanic rocks of the Winterville Formation from the prehnite-analcime subfacies of the prehnite-pumpellyite facies in north-central Aroostook County, Maine, contain an alteration assemblage including chlorite, chlorite/smectite (C/S), analcime, prehnite, and calcite. Field and laboratory study has identified areas where hydrothermal alteration has been pervasive in and around pillows. Compositional, crystal chemical, and structural variations in chlorite appear to be related to distance from this hydrothermal alteration. Samples were studied by whole-rock chemical analysis, electron microprobe analysis of individual mineral grains, X-ray powder diffraction of the clay fraction, and by computer modeling of diffraction patterns to determine the percentage of chlorite in interstratified C/S and to estimate the distribution of Fe and the size of coherent diffracting domains in pure chlorites. Whole-rock and pyroxene compositions suggest that the rocks have undergone Mg metasomatism. Modeling of X-ray diffraction data indicates that the percentage of chlorite in C/S increases to 100%, that Fe atoms become more equally distributed between octahedral sites in chlorite as it becomes more Fe-rich, and that diffracting domains grow larger with proximity to areas of more intense hydrothermal alteration. Analcime also increases near areas of hydrothermal alteration. The areal distribution of hydrothermal effects suggests that the alteration occurred as two separate events, or that two different thermal regimes were active concurrently.

There is evidence in northeastern Maine for at least two glacial phases represented by two tills. The older till unit is the St. Francis, a blue-gray deposit observed in the St. John and Hammond Brook Valleys. At Golden Rapids, the St. Francis till is overlain by a younger brown till with a different clast lithology. The surface of the St. Francis till section at Hammond Brook exhibits a weathered zone, 30 to 45 cm thick, and is overlain by approximately 6 m of stratified sediments. Erratics of Canadian Shield provenance in the surface till indicate advance of the Laurentide Ice Sheet into Maine at least in late Wisconsinan time. Indicator fans, stoss-and-lee forms, drumlins, and striae imply southerly to southeasterly ice flow during the late Wisconsinan maximum. Moraines in southern Aroostook and northern Penobscot Counties and associated outwash and eskers record the northward to northwestward recession of the ice sheet from coastal Maine. Deglaciation in the study area occurred after the formation of the Pineo Ridge Moraine in southern Maine and after the emplacement of the St. Antonin segment of the Highland Front moraine complex of the St. Lawrence Valley in Quebec. A relict ice cap occupied northeastern Maine during the last phase of late Wisconsinan deglaciation. This ice cap had a northeast-southwest trending axis and occupied a perimeter defined by the Aroostook River Valley and by the Fish River, St. Froid, Eagle, Square, Cross, Mud, and Long Lakes. Late Wisconsinan ice flow south of the Aroostook River Valley was generally southeastward. In northern Aroostook County, the flow eventually became northwestward as a consequence of ice drawdown following the incursion of the marine waters into the St. Lawrence Lowland. The radiocarbon age (averaged from several samples) of a sheared and convoluted peat layer associated with a diamicton near Oxbow, Maine, suggests that deglaciation of the area was complete by approximately 10,500 years B.P.

Reconnaissance surficial mapping in the upper St. John River area of northwestern Maine has shown that the latest Wisconsin events in the region were ice-flow reversal and southeastward ice marginal retreat. Widespread erratics derived from the Canadian Shield substantiate ice movement from the west or northwest into Maine prior to these events. Striations, rattails, and small-scale stoss-and-lee forms, all indicating northward and subsequently northwestward ice flow, are superimposed over earlier evidence showing eastward ice movement. Recessional ice-margin positions, delineated by lakes, drainage routes, and moraine segments, demonstrate that the ice margin retreated to the southeast following the emergence of the Notre Dame Mountains as nunataks near the present International Border. Marginal drainage was generally northeastward—perpendicular to topographic slope—via short-lived lakes and spillways. One major stillstand of the ice margin interrupted overall recession in northernmost Maine; however, no conclusive evidence suggests a north or northwestward readvance during this phase. Evidence for north and northwestward ice flow requires a late-glacial dome located over north-central Maine. One explanation for such dome formation is that a late-glacial ice stream developed in the St. Lawrence Valley and drained most of the ice from central Maine before marine calving isolated an independent ice mass. Rapid areal deglaciation ensued with only rare stillstands interrupting extensive disintegration.