Circum-Superior Belt event in Australia and 1,860 million year old magmatism of the Mashonaland event in Africa. The other questionable suggestion related to the Circum-Superior Belt is the existence of a suggested 1,900 million year old global superplume event. The long Labrador Trough, extending from Ungava Bay through Quebec and Labrador, includes two volcano-sedimentary series, the first ranging from 2,170 to 2,140 million years old and second ranging from 1,883 to 1,870 million years old. This magmatism is considered to have formed as a result of back-arc volcanism. The youngest magmatic series (1883-1870 Ma) contains 1,880 million-year-old carbonatites and lamprophyres. 1,883 to
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