Jasper conglomerate

The jasper conglomerate occurs on St. Joseph Island and the St. Mary's River area north and northwest of the Bruce Mines of Northern Ontario, about 65 kilometres (40 mi) east of Sault Ste.

This conglomerate consisted originally of gravelly sands and sandy gravels composed of subrounded pebbles of red jasper, white quartzite, semi-transparent quartz, and black chert, with coarse-grained sand matrix.

The beds of jasper conglomerates fill erosional troughs and channels of what are interpreted to be either alluvial fan or braided river deposits of the Lorrain Formation.

[3][4] Because of its distinctive nature, pebble- to boulder-size fragments of jasper conglomerate can be recognized as glacial erratics in Pleistocene glacial tills and drift within large parts of the glaciated Midwestern United States.

Fragments of jasper conglomerate were eroded by continental ice sheets from Northern Ontario and spread across all of Michigan and as far south as Ohio and Kentucky during repeated glacial advances and retreats.