Complex sentence: Stapleton had taken Sir Henry's old boot because the new unworn boot lacked his scent; the hound had pursued Selden to his death because of the scent on Sir Henry's old clothes.
Split into simpler sentences: Stapleton had taken Sir Henry's old boot because the new, unworn boot lacked his scent. The hound had pursued Selden to his death because of the scent on Sir Henry's old clothes.