Lyle:

I own and operate drilling equipment and use feathers and wedges
along with other materials in quarrying. 

My rough apprehension would be that your dislodged stone was quarried
to rough dimensional size suitable to further dressing/processing for architectural or other ends. Granite has limited applications,
as do all other rocks. And the utility of granites differs among types.

A brief synopsis which may help you follows.
By orienting feathers and wedges perpendicularly to a line,
unfoliated rock can be made to split to the operator's design assuming,
a free face and no interference from transecting differentially
weak mineralization or unexploited cracks. The number of holes drilled,
their width, spacing, depth and penetration of the feathers and wedges in them affords increasing assurance of a full controlled break in
rock of any determined size and composition. A bete noire of drilling is putting your drill steel through a rock into a void. The reasons for this are simple. If it binds--and it very well may--running torque will be translated to the drilling unit or its attendant, often with unfortunate mechanical and human consequence. As well, the drill steel might bend. And it may be difficult to impossible to extract.

Because drilling holes lengthened to a desired breaking point involves more effort, quarrymen will often successfully drill a shorter hole and use proportioned feathers and wedges simply because experience warrants this as sufficient to break rock of a certain type and situation to a greater depth than the hole itself. 

Further,
by plotting two sets of drilled holes to alternatively intersect along
planes at right angles to one another and tapping the feathers and wedges
in alternately along both lines, a 3D break becomes possible.

I am not sure whether some of the holes you
reference show telltale feather and wedge marks nor am I certain which may be split or entire or evidence blast shattering, or may have been abandoned at some stage in a process which never came to full fruition. As a stray footnote, the flat bottom on your holes matches the common pattern of rock drill steels. 

Explosives that may have been employed are a function of temporal
availability, cost, licensing requirements and intended yield product.
Black powder is old tested and true. It, strictly, is a blasting agent
in technical parlance instead of an explosive compound which is defined by brisance or high expansion rate. Deflagrating or blasting agents tend to crack and heave rock with less breakage and in bigger pieces than straight explosives like nitroglycerin, dynamites and others which can fragment rock given suitable loadings and density patterns. In closing,
one last possibility here would depend on the working period of your
quarry. Short of conclusive chemical or other artifacts of blasting,
a very old operation might have employed methods simply dependent on the
regular occurrence of area freezing temperatures.

What you might do for your own benefit is determine the appropriate
state agency responsible for mineral or mining information. Communications with them might specify location, include pictures of the
overall works, measured photos of blocks and working faces in question along with, perhaps, a submitted physical sample of the rock type. 

If your state
has a bureau for these resources and they are disposed to aid, you
may win a harvest of information. County and state historical societies,
building materials groups, industry mining associations and public libraries would also be excellent research resources along with your investigation into property ownership records for areas that intrigue.
A magazine links of potential relevance is www.pitandquarry.com,
www.miningjournal.com and www.stoneworld.com.


I hope this helps. There are many points left unmentioned in the
writing above for sake of brevity and want of comprehensive observations
from your locale. But if you have more, I am sure any ensuing
puzzlements will be graced by an informed response from the list.

Regards,

Edward Hennessey

--- On Thu, 6/9/11, Lyle E. Browning <[log in to unmask]> wrote:

> From: Lyle E. Browning <[log in to unmask]>
> Subject: Rock Holes
> To: [log in to unmask]
> Date: Thursday, June 9, 2011, 6:11 PM
> I've been looking at a series of
> small quarries located in granite beds in the James River,
> Virginia, USA. There are drill holes, blast holes, and
> feather and wedge holes. There's a stone that was split off
> bedrock using feathers and wedges, the piece is about 3 feet
> long, by 18" high by 18" deep and apart from being split off
> the parent rock, hasn't moved. On it are one set of
> horizontal holes on the west and south faces. They are set
> three abreast about 6" down from the top, each being about
> 3" long, half an inch high and cut at a perpendicular to the
> vertical face. They go back into the rock about 3" and taper
> inward slightly and are more or less flat across the back
> end.
> 
> Any ideas on what these things do for a living?
> 
> Thanks in advance,
> 
> Lyle Browning