18 



UNIFORM ITARIANISM AND ACTUALISM 



volcano was more justly a subject of terror to Campania than it has 

 ever been since the rekindling of its fires (Lyell, 1875, Vol. I, pp. 

 654-655). 



This emphasizes the difficulty of giving a strict definition of 

 uniformitarianism. To take the floods: a flood of 1 m high is quite 

 a normal thing. A flood 10 m high is already rather exeptional, 

 when measured against the short experience of our own life span. 

 But we would be at a loss to say if a flood 100 m high was still due 

 to actual causes, if we ever found evidence for such a catastrophic 

 deluge in geological history. Luckily for the geologist this difficulty, 

 as I already indicated above, does not occur in the practical applica- 

 tion of actualism. Floods are normally between 1 m and 10 m high, 

 volcanoes normally destroy only part of their surroundings during 

 one single eruption, and even the worst of quakes are very limited 

 in the areal extent of their damage. Only by continuous repetition, 

 not over short time-spans such as centuries, but over thousands and 

 millions of years, do such major catastrophes in a human sense, but 

 quite minor catastrophes in a geological sense, acquire global signifi- 

 cance. 



Fig. 3. Section through the so-called Temple of Serapis at Pozzuoli, 

 near Naples, showing the various layers with which it has been covered, 

 together with its deepest inundation as witnessed by the boreholes of 

 marine organisms on its pillars (from Lyell, 1875). a b. Ancient mosaic 

 pavement, c c. Dark marine incrustation, d d. First filling up shower of 

 ashes, c e. Freshwater calcareous deposit. / f. Second filling up. A. Sta- 

 dium. 



