The Lg phase generated by earthquakes is used to infer the gross crustal structure of Baffin Bay. The principle of interpretation is that the presence of the Lg phase on an earthquake record is sufficient proof of the existence of continental crustal structure along the entire propagation path, while the absence of the Lg phase is a consequence but not sufficient proof of the existence of a section of oceanic crust somewhere along the propagation path. Examples are given of earthquake records involving propagation paths through three distinct types of gross crustal structure, namely shield-type continental, intermediate-type continental, and oceanic. These examples are used to interpret the records at four seismic observatories located around Baffin Bay for eleven earthquakes, which occurred in and around the Bay in the years 1965 to 1967. The records reveal two areas of Baffin Bay that appear to have oceanic crust, one in the northern part of the Bay at the entrance to Nares Strait, and one in the deep central part of the Bay separated by a bridge of continental crust from Cape York on Greenland to Cape Macculloch on Baffin Island.