Serpentinite beds within the Lalm-Sel area in the Caledonides of central Norway occur as a more or less clearly developed “serpentine conglomerate,” a term used in the literature. This rock is unique because in one locality it contains a rich fauna, determined to an age around the boundary Lower to Middle Ordovician. The serpentinite occurs as beds in a strongly folded eugeosynclinal series of greenschists and phyllite.
The observations and some evidence from recent literature are used in discussing the origin of the “serpentine conglomerate:” tectonic mélange, lava, metasomatic origin, true sedimentary origin, or pyroclastic origin. The latter is slightly favored, mostly from negative evidence: the “conglomerate” must be a sedimentary formation, but a pyroclastic origin seems less impossible than a truly sedimentary one.