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Boothia arch is a northerly trending, Lower Devonian horst in which Precambrian crystalline rocks have risen over 5,000 feet. Cambrian to Lower Devonian clastic and carbonate rocks dip gently away from the exposed basement complex, which rose mainly by vertical movement along major thrust and normal faults rather than by flexure. Northerly trending folds and faults in Cornwallis Fold Belt on Bathrust and Cornwallis Islands and on Grinnell Peninsula are continuations of the Boothia basement structures.
Cambrian to Devonian rocks were deposited over the site of the arch under conditions of quiescence and gradual subsidence; correlative formations in the Franklinian geosyncline are thicker and indicate more rapid subsidence. Principal movement on Boothia arch and Cornwallis Fold Belt is dated by unconformities within the Lower Devonian at three places: (1) on Cornwallis Island the Snowblind Bay formation rests in places conformably and in other places with angular unconformity on Lower Devonian rocks; (2) on Bathurst Island the Driftwood Bay formation lies with angular unconformity upon rocks as young as Lower Devonian and grades laterally into the conformable sequence of Bathrust Island and Stuart Bay formations; and (3) on Prince of Wales and Somerset Islands the Peel Sound formatio variously rests with gradational contact and with angular unconformity on the Middle Silurian to Lower Devonian Read Bay formation. Conglomerates in the Peel Sound formation contain boulders of lower Palaeozoic and Precambrian rocks, and are themselves cut by horst-forming faults.
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