100 Scientific Proceedings, Royal Dublin Society. 
the stamps of Polberro Tin Mine. Each stamp weighs 600 Ibs. 
and is lifted and falls through 9 inches 45 times in one minute. 
Each stamp crushes into fine powder 28 ewt. of tinstuff in twenty- 
four hours. 
Hence, 
Work done in crushing one ae 
cubic foot of rock . = 713°5 ft. cons. 
But, we know that the 
Work done in melting one \ 
cubic foot of ice = 2850°5 ft. tons. 
The latter number is almost exactly four times the former, from 
which I conclude that 
The work done wm melting one cubic foot of we would suffice 
to crush into powder four cubic feet of rock. 
It has been shown that the Geological work done by rain and 
rivers takes 3,090 years to crush and carry to the sea one cubic 
foot of surface rock ; hence we see that one foot of ice (represent- 
ing sun-heat), would account for the present Geological work of 
12,360 years! 
