Rochas pertencentes a formação chamada Belt. Exemplo em Inglês:


De:
http://www.britannica.com/eb/article-9015324/Belt-Series
major division of late Precambrian rocks in North America (the Precambrian lasted from 3.8 billion to 540 million years ago). The series was named for prominent exposures in the Belt Range in southwestern Montana. The thickness of Beltian rocks, which extend northward into Canada, ranges from more than 11,000 m (about 36,000 feet) on the west to about 4,000 m in the east. The upper portions of the…


Parece que a expressão é mantida em Português:

http://www.unb.br/ig/posg/mest/mest104.htm

Adjectivo: Beltiano
690 - BELTIANO

Andar do Precâmbrico IV , definido nos montes de Belt (M. Rochosas, E.U.A.), discordante sobre o arcaico e coberto pelo Câmbrico inferior.
http://www.dct.fct.unl.pt/GGeo/GG680-714.html#690