619
I looked all over for a date and got everything from "early 1800s" to "late 1800s" but nothing exact, so I had to make an educated guess. The first cameras practical enough to take such a photo were developed around 1840 and the excavations began in 1867.
Maybe, between two excavations, the wind has partly filled up the cavity of the previous excavation with sand and thus, the progress wasn't continuous.
This is supposedly from 1867 - 1878:
Wikimedia Commons