As geologists mapped glacial deposits in the late nineteenth century, they became aware that there were several layers of drift, the lower ones corresponding to earlier ice ages.
In the late Middle Ages, it was customary to scrape away the surface of the parchment with an abrasive, which completely wiped out any writing that was there.
在中世纪后期，人们习惯用磨料刮去羊皮纸的表面，把纸上的所有文字都擦得干干净净。
3
None of the European adventurers who wrote up their travels through Asia in the late Middle Ages remark on it.