Upon commencing, in 1847, the special study of the igneous rocks, I, no doubt in common with many others, took for granted the conclusions arrived at experimentally by Professor Bischof, of Bonn, as to the amount of contraction which such rocks would undergo when passing from the state of hot liquidity to that of cold solidity; and I did so, not after any critical examination of the details of Bischof's inquiry itself (the most important of which are contained in a memoir published in Leonhard und Bronn's Jahrbuchfor 1841), but merely in deference to authority, since these conclusions had apparently received unquestioned acceptation from geologists in general.