Complex sentence: Mary Silvina Burghardt's family was part of the very small free black population of Great Barrington, having long owned land in the state; she was descended from Dutch, African, and English ancestors.
Split into simpler sentences: Mary Silvina Burghardt's family was part of the very small free black population of Great Barrington, having long owned land in the state. Burghardt was descended from Dutch, African, and English ancestors.