Last weekend Bowdoin undergraduate students came to Hurricane, and I tagged along as they toured the different pocket beaches around the island. Although all of Hurricane's bedrock geology is granite, there are other types of (mostly igneous) rocks found on the island that traveled over from Vinalhaven and North Haven when the whole region was covered by a large glacier. Glacial till is characteristic because it is unsorted, which means that there are several different clast sizes and many rock types. The Flow-banded rhyolite, pictured below, was found in a pocket beach just east of Gibbon's Point. Flow-banded rhyolite is chemically equivalent to granite, in that it has high amounts of potassium and silica, but it formed in very different conditions.
A professor holds out small clasts of Flow Banded Rhyolite,
