Figure 5. In 1988, an equipment operator at the Crooker Pit called attention to these chunks of mottled reddish-brown and tan clay which had been found in the topset gravel beds of Palmer Hill Delta. Analysis by Joseph Kelley (University of Maine) revealed that this material is a clay mineral called kaolinite, which is rare in Maine and normally found in non-glaciated southern states where rock weathering has continued for millions of years. The most plausible explanation for this occurrence is that pieces of the clay were picked up by the subglacial stream that fed the delta and washed out onto the delta surface. Some of the sticky clay managed to hold together during this turbulent trip, and the fresh well-rounded pebbles found in the clay may have been rolled into it from the surrounding gravel. A possible source for the clay is a bedrock fault zone that crosses the Palmer Brook valley northwest of the delta. The bedrock on both sides of the fault is granitic and could have weathered preglacially to leave a kaolinite residue (Newberg, 1992).

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Last updated on January 5, 2011

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