A 27-year-old male presents to the doctor with complaints of "heartburn" and painful, sour-tasting acid reflux that has not been alleviated by over-the-counter medications. An endoscopic exam is performed and a biopsy of the distal esophagus is taken. Microscopic examination of the tissue shows normal tissue without pathologic changes. What type of mucosa is normal for the distal esophagus?