Across the Great Barrier by Patricia C. Wrede
Scholastic Press, 2011 (first edition); 339 pages
Across the Great Barrier is the second book in the Frontier Magic series, and I think it's better than the first book, Thirteenth Child. The pacing is better--Wrede isn't trying to cover years of Eff's life in 300 pages. Anyhow, this is the story of Eff, who lives on the edge of the frontier in an alternate-history United States. In a world where birth order affects one's magical abilities, Eff is a thirteenth child, which is supposed to be terribly unlucky. But she's also a twin and her twin brother is the seventh son of a seventh son, both of which are very, very good. In Across the Great Barrier, Eff travels into the wilderness beyond the Great Barrier to study the aftereffects of the bug swarms from the first book. She encounters all sorts of magical creatures and continues her study of magic.
I really enjoy this series, although I still want more information. This is an alternate-history world where the American Civil War took place in the 1820s, Thomas Jefferson and Benjamin Franklin were powerful magicians, and no expedition has successfully made it over land to the Pacific Ocean and back. I really want some in-depth historical analysis, which totally isn't the point of the books.