54 SECTIONAL ADDRESSES. 
geology, I should consider this, by itself, as absolutely subversive of the 
first principles of the Huttonian hypothesis.’ . .. ‘The appearance of 
man is a geological phenomenon of vast importance, indirectly modifying 
the whole surface of the earth, breaking in upon any supposition of 
zoological continuity, and utterly unaccounted for by what we have any 
right to call the laws of nature.’® 
Murchison, on the contrary, held that Lyell’s demonstration of the 
unbroken transition between the Pliocene and post-Pliocene had com- 
pletely swept away the arbitrary demarcation between ‘ what had been 
termed the ancient and existing orders of nature.’® 
IJ. Toe FunDAMENTAL PROBLEMS oF 1831. 
The geologists of 1831 worked under the handicap of three fundamental 
uncertainties—the variability of sea-level, the nature of species, and the 
processes that form mineral veins, while progress was hampered by 
theological tradition. 
1. Sea-LEVEL AND THE Mopitiry or THE Crust. 
The most disturbing doubt was as to the level of the sea. The first 
explanation of the occurrence of marine deposits on land was, by an 
obvious analogy, that the tides of some former era had had a longer 
period with a higher ebb and flow. The natural view that the former 
extension of sea over the land was due to a change in the sea was 
adopted by Dante, and was advocated in 1830 in the standard French 
textbook, d’Aubuison’s ‘ Traité de Géognosie.’- D’Aubuison rejected the 
idea that sloping strata had been deposited as horizontal sheets and 
been subsequently tilted. He held that the bedded rocks are still in their 
original positions and their dip is due to deposition upon pre-existing 
slopes. According to him the sea once covered all the highest mountains 
and has been lowered by its reduction in volume instead of having 
been enlarged by water from the interior of the earth. 
The problem of sea-level so exercised the minds of the Geological 
Committee in 1831, that it asked Robert Stevenson—the authority on 
coastal engineering and grandfather of R. L. Stevenson—to report upon 
the erosion of the English coast and ‘ the permanence of sea-level.’ He* 
replied that he had little to add to two previous papers (1816 and 1820). 
The eastern coast of England is still being worn back by the sea; but the 
process is less alarming since it has been recognised that the country 
gains more land by accretion than is being lost by abrasion. The second 
section of the enquiry, the variability in sea-level, is of perennial interest 
as many issues depend upon it. The test case about 1830 was that of the 
Baltic. Celsius in the eighteenth century had remarked that the Baltic: 
appeared to be receding along parts of the Swedish coast; but as the 
sea-level along the German coast had undergone no change since Roman 
times the Swedish evidence was doubted. Leopold von Buch reconciled 
the two sets of observations by the hypothesis that the Swedish coast: 
5 Proc. Geol. Soc., vol. I, 1831, p. 306. 
6 Tbid., 1832, vol. I, p. 375. 
" Rep. B.A., 1831-2, pp. 582-3. 
