the bedrock
breccia
sharp chips · arch rock is made of this
The tell
Angular chips re-cemented into one stone: the anti-conglomerate. Every fragment keeps its corners, because nothing got tumbled round before the rock healed back together. Round pebbles means conglomerate; sharp shards means breccia.
The chips are usually all one rock, broken in place and glued by later minerals, where conglomerate gathers pebbles of everything. The famous one here is the Mackinac Breccia at the Straits: Silurian and Devonian rock that collapsed into the holes left when groundwater dissolved the salt beds underneath it, then healed back together. Look at St. Ignace, Mackinac Island and Bois Blanc.
What it gets mistaken for
- conglomerate
- puddingstone
- concrete
- crackle-veined chert
The facts
- also calledsharp chips · arch rock is made of this
- age~390 million yrs
- classsedimentary
- where it turns upthe Straits · St. Ignace · NOT Arch Rock
- the field markchips are sharp-cornered, never rounded
- on the chartthe bedrock · 1000 stickers ever
Put it on the shelf
Every stone on this chart is drawn and kiss-cut at three inches. The rarer the stone, the fewer exist: only 1000 breccia will ever be printed, then the run is retired.
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