Complex sentence: Tanneries needed a lot of wood to burn, and the lumber supply in the area had been shrinking, so Gray's father used his profits to buy farms in the area, and in about 1823 sold the tannery and became a farmer.
Split into simpler sentences: Tanneries needed a lot of wood to burn, and the lumber supply in the area had been shrinking. So Gray's father used his profits to buy farms in the area and about 1823 sold the tannery and became a farmer.