The sixtieth parallel marks a borderland between the northern and southern worlds. Wrapping itself around the lower reaches of Finland, Sweden and Norway, it crosses the tip of Greenland and the southern coast of Alaska, and slices the great expanses of Russia and Canada in half. The parallel also passes through Shetland, where Malachy Tallack has spent most of his life. In Sixty Degrees North, Tallack travels westward, exploring the landscapes of...