The Waterville Formation: A Well Known Central Maine Bedrock Type
https://docs.google.com/document/d/1OIU089B_n15dthsK_sFSsb-IQZB4B3XoLc6NbZEPH5s/edit An unusual exposure of the Waterville Formation. Blasting revealed a vertical view showing the slightly tilted layers. This outcrop is visible along I-95. Note: Geologists must be given permission by the DOT to explore rocks along I-95!
Vassalboro Group rocks are found throughout Central Maine (from well northeast of Bangor all the way to southwest of Portland) You will see a couple of rock formations that belong to this group along the trails: the Waterville Formation and the Mayflower Hill Formation
The Waterville Formation can be found from Lagrange southwestward through Corinna and Pittsfield into Waterville and Manchester. It is mainly dark gray slate or phyllite, with thin layers of light gray siltstone or sandstone. Formations of similar rock content are found in Western Maine and Northern Maine.
More than Slate!
The rocks near Waterville west of the Kennebec River were named the Waterville Shale way back in 1925. University of Maine professor Phil Osberg renamed these rocks the Waterville formation in 1968. He did this because the Watervale shale consisted of a distinct set of rock types, not just shale.
Osberg also noticed other details about composition of the Waterville Formation. In the Eastern Part there were thin beds of quartz mica and metamorphic rocks known as quartzite between the slate layers. On the west side of the formation layers of limestone and metamorphic rocks known as phyllite and wackes were present. Phyllite is the beautiful shiny rock that is exposed in a few places around Waterville and Winslow. Wackes are sometimes called dirty sandstone because unlike regular sandstone these rocks contain a mixture of fragments of other rock and mineral types that formed in a matrix of sand and mud.
Garnet, mica, and other minerals are also found. When you see these shiny minerals embedded in the slaty rock it tells you this area experienced a high degree of heat and pressure during its formation.