8 PRINCIPLES OF PALEONTOLOGY. 



of all inquiries, both in the domain of geology and that of 

 palaeontology. The advocates of continuity possess one im- 

 mense advantage over those who believe in violent and revo- 

 lutionary convulsions, that they call into play only agencies 

 of which we have actual knowledge. We know that certain 

 forces are now at work, producing certain modifications in the 

 present condition of the globe ; and we know that these forces 

 are capable of producing the vastest of the changes which 

 geology brings under our consideration, provided we assign a 

 time proportionately vast for their operation. On the other 

 hand, the advocates of catastrophism, to make good their 

 views, are compelled to invoke forces and actions, both de- 

 structive and restorative, of which we have, and can have, no 

 direct knowledge. They endow the whirlwind and the earth- 

 quake, the central fire and the rain from heaven, with powers 

 as mighty as ever imagined in fable, and they build up the 

 fragments of a repeatedly shattered world by the intervention 

 of an intermittently active creative power. 



It should not be forgotten, however, that from one point of 

 view there is a truth in catastrophism which is sometimes 

 overlooked by the advocates of continuity and uniformity. 

 Catastrophism has, as its essential feature, the proposition that 

 the known and existing forces of the earth at one time acted 

 with much greater intensity and violence than they do at pre- 

 sent, and they carry down the period of this excessive action 

 to the commencement of the present terrestrial order. The 

 Uniformitarians, in effect, deny this proposition, at any rate as 

 regards any period of the earth's history of which we have 

 actual cognisance. If, however, the " nebular hypothesis " of 

 the origin of the universe be well founded as is generally ad- 

 mitted- then^ beyond question, the earth is a gradually cooling 

 body, which has at one time been very much hotter than it is 

 at present. There has been a time, therefore, in which the 

 igneous forces of the earth, to which we owe the phenomena of 

 earthquakes and volcanoes, must have been far more intensely 

 active than we can conceive of from anything that we can see 

 at the present day. By the same hypothesis, the sun is a 

 cooling body, and must at one time have possessed -a much 

 higher temperature than it has at present. But increased heat 

 of the sun would seriously alter the existing conditions affect- 

 ing the evaporation and precipitation of moisture on our earth ; 

 and hence the aqueous forces may also have acted at one time 

 more powerfully than they do now. The fundamental prin- 

 ciple of catastrophism is, therefore, not wholly vicious ; and 

 we have reason to think that there must have been periods 



