The island is of volcanic origin; the only signs of upheaval are raised limestone beaches in the extreme N.
There is evidence that Ungava, like the rest of Labrador, has risen several hundred feet since the Ice Age, marine beaches being found up to 700 ft.
As these lakes shrank after the return of an arid climate, they left elevated beaches and deposits of various minerals, which mark their former extent.
In post-Glacial times, a subsidence admitted the sea into the Lagan valley and across the eastern shore in several places; but elevation, in the days of early human occupation, brought these last marine deposits to light, and raised the beaches and shore-terraces some 10 to 20 ft.
The Upper Devonian was a period of marine retreat; the crustal disturbances of the Lower Devonian were renewed and great quartz-pebble beaches were formed on the rising shore lines, producing the West Coast Range conglomerates of Tasmania, and the similar rocks to the south-east of Mansfield in Victoria.