Westboro Formation

Westboro Formation - Quartzite, schist, calc-silicate quartzite, and amphibolite. Consists of quartzite and argillite in Saugus and Lynnfield areas. Westboro Formation consists primarily of orthoquartzite and subordinate mica schist, calc-silicate rock, amphibolite, and quartzitic biotite gneiss and schist. Westboro as portrayed by Nelson (1974), Bell and Alvord (1976), and Hepburn and DiNitto (1978) are correlative [with varying certainty]. West and south of Boston, disconnected masses of quartzite and associated rocks are shown on State bedrock map by Zen and others (1983) as Westboro although not continuous with belts mapped by Nelson (1974) or Hepburn and DiNitto (1978). Includes isolated quartzite masses mapped by Castle (1964) in Reading area. On State bedrock map, arbitrarily includes thin quartzite mapped as Burlington Formation by Bell and Alvord (1976) because the units are similar and to reduce number of small units on State map. Rocks mapped as Rice Gneiss by Nelson (1974) were included in unnamed metamorphosed mafic and felsic volcanic unit on State bedrock map, but author now feels it should be either a part of Westboro, or a separate unit below it. Westboro in Framingham area and to the northeast is overlain by unnamed assemblage of metamorphosed mafic and felsic volcanic rocks. South of town of Westborough, Westboro is truncated by Bloody Bluff-Lake Char fault system. Intruded by Proterozoic Z batholithic rocks. Equivalent to Plainfield Formation of eastern CT because it lies in same strike belt, and is probably equivalent to Quinnville Quartzite and unnamed mica schist and phyllite of Blackstone Group. Contact between Westboro and Blackstone is arbitrary on State bedrock map on basis of proximity of isolated exposures of the two units to their respective type areas. No area of continuous exposure exists between Westboro and Blackstone (Goldsmith, 1991).