The Bouguer gravity anomaly map of western New York State and Lake Ontario indicates a series of gravity anomalies extending north-northeast across New York State and Lake Ontario. These gravity anomalies are due to the extension of the Precambrian rocks of the Bancroft-Madoc area of southern Ontario, Canada. Mafic plutons intruded into a mafic-metavolcanic sequence produce gravity positives, while granitic batholiths cause negative gravity anomalies. The intermediate gravity values are due to a marble-rich metasedimentary group. In most places the gravity positives are located between a magnetic high and low, suggesting the center of the magnetized source is fairly identical with the center of mass surplus.

The Clarendon-Linden fault is the most prominent structural feature in the Paleozoic rocks of western New York. Some control of this Paleozoic structure by the Precambrian basement is suggested

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by the location of the structure on the western flank of a series of gravity and magnetic positives. High resolution seismic reflection profiles, gravity, and magnetic-intensity data indicate the structure continues under Lake Ontario into Canada. The geophysical anomalies also suggest the fault has a northwest branch near Attica, NY, which may account for the moderate seismicity between Attica and Buffalo. The mafic intrusions associated with the fault probably indicate fracture zones in the Precambrian basement. The potential of these fracture zones for generating earthquakes in the area is of major concern in nuclear power plant site location.

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