The Chamberlain's Brook Formation is a thin but distinctive geologic formation of dark red calcareous mudstonesNormore, L. S. 2012: GEOLOGY OF THE RANDOM ISLAND MAP AREA (Nts 2C/04), Newfoundland. Current Research (2012) Newfoundland and Labrador Department of Natural Resources Geological Survey Report 12-:121–145. that crops out from Rhode Island to Massachusetts and, Nova Scotia, New Brunswick and Newfoundland. It preserves fossils, including trilobites, dating back to the lower mid-Cambrian period. Its lowermost member is the Braintree Member (lowest Middle Cambrian) and the uppermost member is the Fossil Brook Member.
See also List of fossiliferous stratigraphic units in Massachusetts Paleontology in Massachusetts Inlet Group
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