Hi,
Are you sure of the date on the tombstone? There was no death registered in Cheshire for a Thomas Graham in 1866 but there was one in 1864 which matches the following report I found:
Cheshire Observer, Saturday 16th July, 1864
FATAL ACCIDENT TO A PLASTERER AT BIRKENHEAD
A melancholy and fatal accident took place on Tuesday afternoon at the Birkenhead dock works, to a mason named Thomas Graham aged forty. At the northern entrances, where nearly 2,000 men are employed in building the immense blocks of masonry, the larger stones are removed and set by “jennies” travelling upon stages about 40 feet high from the foundation. One of these “jennies” was removing some stones, when it came in contact with a diagonal piece of timber which binds the stage together. This piece of timber sprung from its fastenings and fell upon Graham, crushing him down upon the wall where he was at work, and he expired almost immediately, in the arms of his son, who was employed within a few yards of him. Graham was a very steady, industrious workman, a native of the neighbourhood of Annan, and had been employed for many years on the Liverpool and Birkenhead dock works. The occurrence appears to have been purely accidental.
Regards,
Mo