54? Geological Society. 



are among the last, and not the first steps of systematic know- 

 ledge. Equally true, and far more salutary is the lesson that sci- 

 ence cannot be advanced by equivocation. As in trading con- 

 cerns fixed weights and measures are necessary guards against 

 fraud, so in philosophical investigation words of definite meaning 

 are indispensable securities against sophistry and self-delusion. 

 Euclid did not end, he began with defining. Mathematical certainty 

 has no other basis than mathematical precision, and the greater part 

 of those absurdities which from time to time attach themselves to 

 all other branches of knowledge derive their subsistence from am- 

 biguity of language and a dearth of definition. 



A torrent brings down a quantity of alluvial matter, and the plain 

 on which it rests is said to be elevated. 



An opening occurs in the earth ; ejected ashes, scoriae and lava 

 accumulate around it ; a Monte Nuovo is formed ; and the area it 

 occupies is said to be elevated. 



By the persevering labour of polypi, a coral reef gradually attains 

 the surface of the ocean ; and the fabric so constructed is said to be 

 elevated. 



A porous rock covers a rock that is not porous; the rain filters 

 through the superincumbent bed; springs break out in the sub- 

 jacent ; and at last, for want of support, the porous rock, ori- 

 ginally horizontal, acquires an inclined posture, one end being di- 

 rected upwards, the other downwards ; and the whole is said to be 

 elevated. 



An earthquake takes place at the mouth of a river; the sea is 

 violently affected ; a bar is formed at the entrance of a harbour 

 from the washing in of new alluvion, or from some obstruction to 

 the escape of the old; where a ship floated, a barge is aground ; and 

 the land is said to be elevated. 



Such instances of Elevation are common and incontestible; but 

 elevation of this kind is quite different from that which forms the 

 subject of my present inquiry. 



By the term Elevation, I mean only the removal of any given ob- 

 ject from a lower level to a higher level; consequently it is neces- 

 sary, before I speak of an object as elevated, that I should be pre- 

 pared to show two things : first, the level at which it has stood ; 

 secondly, the level at which it stands. 



That I might form a right opinion of the theory, the merits of 

 which I am about to investigate, I have endeavoured to determine 

 the site, the number and the magnitude of those multifarious objects 

 to which the attribute of elevation is continually applied. The at- 

 tempt has proved unsuccessful: they are indefinite in place, in form, 

 and in dimension. That Mountains should be elevated is not sur- 

 prising, but we are familiarized also with Valleys of elevation*. In 

 ancient times an Island (Delos, for example,) would alternately 



* Valley* of this nature are properly called by Mr. Scropc '* valleys of 

 " elevation and subsidence," or more concisely, " anticlinal valleys." See 

 Scrope on Volcanoes, p. 213. 



