Ultrabasic intrusives have been problem rocks for many years, but, of late, interest has centered around the later changes that have taken place in these rock masses. The chief item is the autometamorphic or exometamorphic origin of the serpentine derived from them; in other words, the question is, did the solutions producing change come from outside the masses themselves or were they indigenous to the original magmas?
The Vermont ultrabasics are a series, exposed under conditions peculiarly favorable for study.1 Some of the best exposures are in verde antique marble quarries, where structural detail of the stone shows to advantage on the walls. Mapping of practically all similar intrusives, in a belt extending from the asbestos district of Quebec southward into Massachusetts, has been done on an extremely detailed scale, and surface exploration was supplemented by diamond drilling on many of the serpentine bodies. . . .