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
Circum-Baikal Railway in operation: Kultuk, Maritui, Ulanovo, and Baikal, with one section of double track at 137 km. The Circum-Baikal contains thirty-eight tunnels with a total length of 9063 m (the longest of them, a tunnel through cape Polovinnyj, is 777.5 m long). There are also 15 stone galleries with a total length of 295 m and 3 ferro-concrete galleries with apertures, 248 bridges and viaducts, and 268 retaining walls. The Circum-Baikal has no equal in Russia as to the richness of engineering constructions. The tunnels and stone galleries of the Circum-Baikal are unique in that they were constructed atypically and have