What you're looking at is an ancient continent called Laurencia

You're seeing an ancestral continent called Laurentia, which grows over the next few hundred million years as island chains collide with itand add land mass. We're now at 400 million years ago. Off today's east coast, the massiveAfrican plate inches westward,closing the ancient Iapetus Ocean.It finally collides with Laurentia at 250 million years to form another supercontinent Pangea.