This is an Irish geologist mentioned recently in "Buz's refutation of all radioactive dating methods" - John Joly, who worked in Trinity College Dublin.
http://www.irishmidlandsancestry.com/...people/joly_john.htm
Here's a nice paragraph from it:
"One of his claims to fame was the making of an accurate estimate of the age of a geological period - an essential step in estimating the age of the Earth. Working in collaboration with Sir Ernest Rutherford in Cambridge, and using the decay in radioactivity in minerals, he estimated, in 1913, that the beginning of the Devonian period - the geological period between the Silurian and Carboniferous - was not less than 400 million years ago, an age which is in line with that accepted to-day. This makes the Earth about 4,500 million years old. A previous Trinity academic - Archbishop James Ussher - using chronological information in the Bible, had estimated the date of creation as 4004 BC!"
The Rock Hound