Two historians have published a book that examines slavery in New York’s Hudson Valley. Susan Stessin-Cohn, of New Paltz, and Ashley Hurlburt-Biagini, of Salisbury Mills, spent years researching the topic for “In Defiance,” recently published by Albany-based Black Dome Press. Their book contains more than 550 newspaper notices published between 1735 and 1831, four years after slavery was abolished in New York state. Most of the notices were published in…