Drill marks

slowburner

Here are two pictures of the two halves of a stone that was split by drilling and insering either 'plug and feathers' or wooden wedges made to swell with water.

• Would anyone know what period drill marks like these are associated with?
• And can anyone suggest how they were drilled?

They certainly aren't as regular as contemporary drill marks and they seem to taper to a point, unlike contemporary drill holes. I was always under the impression that holes like these are modern but reading a CRDS report on Carrickmines I noticed a very similar bore hole which was attributed to the Medieval period.
Failing answers to the above, could anyone point me towards an online resource which might have relevant information?

Fuzzy Clam

Looks similar to the method used in the construction of Dunlaoghaire harbour.

slowburner

My limited knowledge extends to the fact that there were two or three methods for splitting granite which gives results like those pictured.
Oldest first.

• Holes are bored along a line, wooden wedges are inserted and soaked with water, usually over night. As the wedges swell, they split the rock along the line.
• Plug and feathers - two feathers, like two halves of an iron tube, are inserted into pre-drilled holes, as above. Then the 'plug' - a massive nail or chisel - was driven in between the two feathers, forcing the rock apart.
• Explosive. Does what it says on the tin really.

What I am after is a way or pointer to a methodology of approximate dating for these sorts of drill marks in Ireland. They are abundant in Ireland, just as you saw in Dun Laoghaire. I presume that someone, somewhere has studied them?
I've not found anything suitable on the web. Searching for early drilling methods keeps bringing me back to ancient Egypt and wild theories like the Egyptians boring holes with ultrasound :eek: