Lloyds report posted by danthecavingman was our primary document when contemplating taking on the project.
In Fig. 111 of the report Lloyd mentions the height of the arch that leads into the Main Chamber at 'B' as being +/- 3 yards. Some of the measurements he gives of the Main Chamber are a little over exaggerated, but when all you have is a candle you might expect this. The +/- 3 yards though, you would think as being fairly accurate and easily within view. Today, the arch is less than a yard. The depth of the main shaft should have been easy to measure fairly accurately.
When members of the Eldon dug down in the area approx. 2 yards upslope of 'T', near the bottom of the Main Chamber, they hit a solid floor at +/- 8' suggesting that approx. 8' of additional rock has been thrown in (or otherwise deposited) since Lloyds visit. We removed a fair number of sizeable tree branches from about 5' depth in the very small area we were digging on Sunday so over the whole area of the bottom of the Main Chamber this could possibly account for some of the volume.
The report suggests that it was not too many years before Lloyds visit that the elusive second shaft was actually descended for some vast depth before reaching water.
It could well be that there isn't the vast amount of rock as Lloyd suggests in Fig 111 at all, he probably assumed it had a flat floor whereas the reports of descending the second shaft talk about steep ledges leading into it. In the area around the dig site, there might actually only be about 10' of rock to clear out before you find the old oak timbers that the miners most likely placed around the much narrower descending second shaft. If they actually did?
The bottom of the shaft we are currently digging (see MarkR's BBPC link with photographs) should be below this point within only a few weeks.
I am though, forever the optimist.
I do think, for the sake of consistency with Lloyds reporting, we should use imperial units in our reports. That'll confuse the therionists.
Mark