I have seen this experiment and also the video. However I am not convinced that the block being drilled in the photograph and certainly the video is actually granite...
The final photograph in the series showing a completed drilled hole is in fact an ancient artifact complete with the mysterious striations.
Still photographs cannot be evidence of a process. I rather think that what we are looking at is a series of still photographs of a drill and ancient drill holes being used to illustrate an hypothesis.
Here is a video of Stocks drilling what is clearly soft limestone. I cannot find an equivalent video demonstrating this process on hard granite.
He also refers to the work piece as "stone" or "solid rock".
He does not specify the type of stone. Which is of course of huge importance.
Do you know of a video, moving image of granite, copper and bow drilling.??
Post Edited (02-Apr-15 10:12)