She also found significant support and extensive evidence from a group of biodynamic agriculture organic market gardeners, their adviser, Dr. Ehrenfried Pfeiffer, other contacts, and their suite of legal actions (1957-1960) against the U.S. Government. According to recent research by Paull (2013), this may have been the primary and (for strategic reasons) uncredited source for Carson's book. Marjorie Spock and Mary T. Richards, of Long Island, New York, contested the aerial spraying of dichlorodiphenyltrichloroethane (DDT). They compiled their evidence and shared it with Carson, who used it, their extensive contacts, and the trial transcripts as a primary input for "Silent Spring". Carson wrote of the content as "a gold mine of information" and says, "I feel guilty about the mass of your material I have here" and makes multiple references to Pfeiffer and to his correspondence.