Complex sentence: Inside the mound, archaeological researchers have discovered Adena Hopewell remains and ornaments, along with a small sandstone tablet, the Grave Creek Stone, believed by modern scholars to be a hoax.
Split into simpler sentences: Inside the mound, archaeological researchers have discovered Adena Hopewell remains and ornaments. In addition, they discovered a small sandstone tablet, the Grave Creek Stone, which modern scholars believe to be a hoax.