When Sach runs into the cave, he hits and falls over a boulder. The boulder shakes and moves like it was made of something much lighter than rock, which it was.
The second time Sach is under hypnosis - and speaking as his "past life" self, a colonial tax collector from the 1600s - he mentions a distance as being in kilometers. But the term wasn't invented until the metric system was adopted by France in the 1790s.