Complex sentence: Big Rock is a glacial erratic that is part of a long, linear scatter of thousands of distinctive quartzite and pebbly quartzite glacial erratics between and in length that known as the Foothills Erratics Train.
Split into simpler sentences: Big Rock is a glacial erratic that is part of a long, linear scatter of thousands of distinctive quartzite and pebbly quartzite glacial erratics between and in length. This linear scatter of distinctive quartzite glacial erratics is known as the Foothills Erratics Train.