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The Beaver Creek area is a zone of intensely folded metamorphic rocks of the Grenville Complex in the Grenville lowlands northwest of the Adirondacks in New York. The area underwent regional metamorphism to the upper amphibolite facies about 1 b.y. ago. Pegmatite, granite, and gabbro intruded the region essentially syntectonically. Recurrent faulting that was initiated early during tectonism has separated the area into distinct structural domains. Shallow intrusion by diabase occurred in the Late Proterozoic or Early Cambrian (Brown, 1983) after many kilometers of rock were eroded. The diabase formed dikes that trend northeastward, but are not obviously aligned with the northeast-trending folds, faults, and layering in the host rock. They intrude many rock types of the Grenville Complex. Some dikes are alkalic (Brown, 1975), amygdaloidal, and have chilled borders. If they reached the surface, the resultant effusive rocks have not been preserved. The dikes are truncated at the unconformity beneath the overlying Upper Cambrian Potsdam Sandstone. The Potsdam Sandstone is essentially flat lying and occurs mainly as thin outliers of Paleozoic rocks that now are northwest and west of the Beaver Creek area. Many small sandstone bodies fill low areas and cavities in the marbles beneath the unconformity. The sand probably was derived from the Potsdam Sandstone, but might also represent siliceous sediments that were deposited and stripped away prior to deposition of the Potsdam. Some Potsdam outliers have been faulted and warped and it is not known whether this deformation results from slumping in areas of dissolved carbonate rock or from a late tectonic event (Brown, 1983, p. 4). There is evidence for both processes, but neither has affected .the major tectonic features of the rocks of Proterozoic age.

Geologic map of the Beaver Creek area in the Grenville Lowlands, St. Lawrence County, New York