ways, the most likely being, the deposition of carbonate of lime 

 from' its solution as bicarbonate through any cause that would 

 expel the excess of carbonic acid. 



« Eruptions of the fluid igneous matter in the interior, have from 

 time to time broken through the overlying strata, just as at the 

 present day (though possibly on a modified scale) similar outbursts 

 are produced by volcanic action." * 



It is necessary to be very careful not to attribute entirely to any 

 one cause alone the changes that have taken place, for analysis 

 shews that whilst many of our granites are undoubtedly of igneous 

 origin, others are true sedimentary beds altered by metamorphic 

 action, and experiments in the laboratory tend also to show that 

 this metamorphic action was due to the combined effects of a heat 

 considerably under that of fluidity, great pressure, and water. 



It has up to within very recently been thought that all the 

 characteristics of metamorphism were due to contact with the 

 interior heat of the earth, but this idea must now be received with 

 considerable caution. It has been proved beyond doubt that the 

 sum of the actual and potential energy in the world is constant, 

 and Dr. Joule has exhibited experimentally the measurable relation 

 between heat and gravity. He has determined that a certain 

 amount of one kind of motion produces an equivalent quantity of 

 another kind. He proved that 772 pounds of matter falling one 

 foot gives rise to enough heat to raise a pound of water one degree F. 

 in temperature. In like manner the mechanical force expended in 

 such eff'ects as the compression, crumpling up, and consolidation of 

 strata, would give rise to a corresponding development of heat, and 

 consequently of chemical action, more than sufficient to completely 

 alter the character of immense rock masses. 



The origin of metallic veins is still involved in mystery, the 

 fact of their always lying either due north and south, or east and 

 west, as the case may be, is sufficient proof that they are not due 

 alone to volcanic action, and points rather to electro-magnetic 

 influences. Each metal has its particular direction, and so 

 invariably is this a rule that a miner, if he finds a vein going east 



• David Forbes, F.R.S. 



