Circum-Superior Belt northwestern Superior craton margin intrude an older, 2,090 to 2,070 million-year-old dike swarm. The Ospwagan Group is younger than and the 1,864 million-year-old Winnipegosis komatiite belt lies to the southwest. Numerous tectonic settings have been suggested for triggering magmatism in the Fox River Belt, including a marginal basin rifting event. At the southern portion of the Circum-Superior Belt, a group of fragmental sediments composed of iron formation was formed during a period of magmatic activity in the Marquette Range Supergroup. Included in the Marquette Range Supergroup is the Hemlock Formation, a bimodal volcanic group that is estimated to have an
Ring of Fire (anthology) "topnotch choice for alternate history fans and essential for libraries owning 1632 and 1633" and that these "15 stories contribute directly to the main plot lines of the series and illustrate the complex and multifaceted nature of historical fiction." Ring of Fire was listed on the Locus (magazine) Hardcovers Bestsellers List for two months in a row during 2004, topping at number 2. Ring of Fire (anthology) Ring of Fire is the third published book by editor-author-historian Eric Flint of the 1632 series, an alternate history series begun in the novel "1632" (February 2000). The "Ring of Fire" is both