TY  - RPRT
TI  - Aeromagnetic map of the Ayer quadrangle, Middlesex and Worcester Counties, Massachusetts
AU  - Members of the Engineering Geology and Ground Water Branches, U.S. Geological Survey
PY  - 1971
DO  - 10.3133/gp741
UR  - https://pubs.usgs.gov/publication/gp741
ID  - gp741
ER  -