A reconnaissance refraction survey was conducted on the Grand Banks, St. Pierre Banks, Cabot Strait Trough, and Banquereau. Three stations on the Grand Banks indicate sedimentary layers ranging from 2300 to 10,700 feet in thickness. The sediments are underlain by basement rocks having velocities of 16,150–18,200 ft/sec.

A striking feature, existing on a profile running from St. Pierre Bank across Cabot Strait Trough to Banquereau, is the occurrence under the trough of a prism of sediments that thickens to almost 14,000 feet near the northeast margin where it is almost entirely truncated by basement rock.

The sequence of subsurface layers found on the banks south and southeast of Newfoundland is not unlike that reported for the submerged shelf off the northeast coast of the United States and the banks off Nova Scotia. The seismic results and the recent results from dredging and coring operations support the hypothesis that the shelf off eastern North America is a depositional feature dating back to at least Lower Cretaceous time. The physiographic differences north and south of Cape Cod are believed to be due to erosion. The data suggest a structural origin for the Cabot Strait Trough, although the possibility of subsequent modification by glaciation is not ruled out.

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