Jules Verne 
The Fur Country [EPUB ebook] 

In this book, a party sent out by the Hudson Bay Company build a fort upon what they believe to be an island, but, upon discovering, after a while, that the sun has totally changed its place of rising, they find that they are really upon a floating ice-floe, and this gradually dwindles in size, frightening the voyagers, and bringing into play all their ingenuity.
This book is, without question, the most readable wonder-story in modern literature