The Bowder Stone

I'm always a sucker for notice boards like this. The volume measured in "solid feet" caught my eye. How can we model the volume from the data for such an irregular shaped block? Given the circumference and perpendicular height, I have decided to try using a cylinder. Circumference = 2*pi*radius. So radius = 89/2*pi = 14.1 feet. Area = pi*radius-squared = 630 square feet. Volume = area x height = 22691 cubic feet, to too many sig figs. Almost right. An Internet conversion device gives the value mentioned on the board as 651 cubic metres. In the old UK measures, there were 20 hundredweight (cwt) in a ton.So there were 1971.65 tons. This is 1971.65 x 1016.047 = 2.003 million kg. The density of the rock is therefore = 2.003 million/651 = 3077 kg per cubic metres. Try an Internet search for porphyritic greenstone. It seems to come up in very ancient references from about the date of this notice. But the density is right for the top end of basalt. It should be too high for granite. It also seems too high for andesite which is the most common rock type I come across.