444 Mr. J. Stevenson on the Chemical and 



But another difficulty in the way of accepting our theory 

 is raised by the question as to whether it is possible or 

 probable that the whole crust of the earth for several miles 

 of its thickness should be heated after its first solidification 

 to a temperature sufficiently high to produce metallic iron 

 from oxides and silicates and other compounds of iron through 

 the reducing action of carbonaceous matter, and also to- 

 liquefy the rocks so as to allow the metallic iron to sink down 

 to an inaccessible depth. We know sufficiently well that 

 all through geological history down to the present day certain 

 portions of the crust — the seats of volcanic action — have been 

 heated to this extent, but as regards the area and depth of 

 these portions or regions, and the quantity of material heated in 

 each case, our information is very limited. However, judging 

 from what we may roughly infer regarding the prevalence of 

 volcanic action both in our own times and in past geological 

 history, we should say that the total amount of volcanic action 

 has probably not been sufficient to heat up the \\ hole crust 

 of the earth to the extent required for our theory. At any 

 rate, we should say with a fair degree of certainty that the 

 total volcanic action on the earth, as inferred from geological 

 observation , would not be sufficient to heat up the whole 

 crust of the earth (in portions at a time of course) repeatedly 

 to the fluid condition, as would require to be the case if the 

 amount of carbonaceous matter has always averaged con- 

 siderably less than ^ per cent. But on the other hand 

 it is quite possible that the condition* atfecting the prevalence 

 of volcanic action or heating operations were very different in 

 very ancient times from what they have been during known 

 geological epochs. "W hen the surface of the earth first became 

 solid the underlying rocks must have been very hot, perhaps 

 liquid in many places ; but even if they were solid they must 

 have been near the fusing-point, and therefore volcanic eff j cts 

 must have been more easily produced then than now. Further, 

 the low degree of conductivity for heat possessed by ordinary 

 rocks has, at this point, an important bearing on the question 

 before us. Lord Kelvin in his essay on the 'Age of the Earth ' 

 gives expression to the opinion that vegetation or some kind 

 of organic life may quite well have begun very soon after the 

 surface of the earth first became solid, and it is easy to see that 

 any vegetable or other organic remains deposited in those very 

 early epochs would not have much chance of remaining in 

 a comparatively unaltered condition for a great length of 

 time, as the sedimentary rocks of that epoch would be liable 

 to be heated to a high temperature within a comparatively 

 short period after their deposition. Also we should expect 



