Most of Mirror Lake is underlain at shallow depths by glacial deposits (materials that were deposited by glaciers during the ice age), but parts of the lake are in direct contact with the bedrock. Bedrock is exposed at land surface near the beach and across from the beach at “swimming rock”.

Bedrock at Swimming Rock

Throughout the Mirror Lake watershed, indeed throughout Hubbard Brook valley, bedrock underlies the glacial deposits or it outcrops at the land surface. The swimming rock is a typical piece of what was once called “Littleton Formation”, a quartz-schist that resembles a twisted, gray, layer cake. This generic, metamorphic bedrock type has been divided into several sub-sections, and this particular piece is now called “Lower Rangeley Formation”. Eons ago, this was probably oceanic beach sand, thus it is primarily composed of silicates.

More to come...