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conglomerate - hand/display specimen of conglomerate derived from the Franciscan-Knoxville sequence

$ 7.50

The Mesozoic Franciscan-Knoxville sequence is a series of mostly metamorphic rocks characterized by serpentine, various cherts, shale and graywacke from which this conglomerate is derived. This accounts for the overall greenish hue of the clasts. Clast is derived from the Greek klastos, broken, and refers to the rock fragments that make up sedimentary rocks.

This conglomerate was collected from the bed of Perkins Creek under the assumption that any conglomerate that had gotten that far would withstand student examination in a classroom. The source formation is uncertain.

The clasts in this conglomerate, originally loose pebbles in a stream channel, were stranded when the channel changed position, became buried, lithified into a conglomerate which was then uncovered, weathered and eroded. Chunks of conglomerate were then carried down the Perkins Creek drainage. The angular nature of many of the clasts it is composed of shows that the pebbles that make up this conglomerate have not traveled very far. 

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