Abstract

In the spring of 1923 the writer had opportunity to collect a suite of igneous rocks from Monhegan Island. According to Lord,1 their considerable variation in composition is chiefly due to differentiation, in place, of a deep seated basic magma. He sees in the amphibole reaction-rims between feldspar and both olivine and diallage some evidence of regional metamorphism. Though these reaction-rims may be susceptible of other interpretations, the main idea of differentiation seems tenable.

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