33 PROCEEDINGS OF THE GEOLOGICAL SOCIETT. 



guide to rational geology. M. ThurmanTi's * elaborate classification 

 of the strnctiiral features of the Jura seems to have led to no fur- 

 ther conclusion than that the contortions were produced by lateral 

 pressure. 



One must have visited alpine regions fully to understand how in- 

 dispensable palaeontology is to the field geologist. It would be all 

 but impossible to discover the structure rof many large areas (and 

 how much more so to assign the appropriate relative ages to the 

 several rock-groups !) without the siu^e criterion of the fossil remains. 

 But it must not be forgotten that this bare structure and these 

 relative ages are but a portion of the mere data upon which a geo- 

 logical history of the region is to be founded. 



It has often occurred to me that geologists are guilty of a general 

 inconsistency in taking so little account of subsidence in the dis- 

 cussion of phenomena of disturbance. Subsidence is often intro- 

 duced to admit of the continued accumulation of deposits ; but, 

 to account for the disturbance of strata, upheaval and intrusion 

 are the agencies commonly appealed to. Yet in the most generally 

 accepted theory of geogeny, the dominant character is shiinking and 

 the consequent depression of the surface. The leading speculations 

 upon crust -movementsjiave indeed proceeded from the point of view 

 of this theory; but I am now alluding to the lesser featm^es of 

 disturbance — the dips and strikes which form the elements of actual 

 observation. If that theory be true, the features resulting from 

 depression should greatly predominate in the detail-structure of the 

 earth's crust. I am far from insisting that d-priori views should 

 regulate rigidly our interpretations of phenomena. It would, on 

 the other hand, be more in accordance with rational methods of 

 research that those views should be taken into account, if it were 

 only for the pui'pose of verification. In the case of the grand 

 cosmological speculation of Laplace, the study of the earth's structure 

 is almost the only direct test we can apply. The opposite course 

 has been adopted : not only have the suggestions of this theory been 

 disregarded, but the positive indications of mechanical laws have been 

 set aside to warp observations into agreement vrith our superficial 

 prepossessions. Many a scientific man cannot see a hill without 

 taking for granted that it has been upraised, and attributing all its 

 features to that process. In the particular case before us, the con- 

 tortion of the ]Vrolasse is to this day the accepted proof of the last and 

 greatest upheaval of the Alps. It can scarcely be necessary to say that 

 such contortions can only indicate yielding, and hence an equivalent 

 settlement of the mass from which the pressure is communicated. 

 Plexares may, indeed, accompany an upheaval ; but if so they must 

 be a negative element in the total ; and it is stepping beyond the 

 limits of legitimate inference to take them jprimd facie as evidence 

 of upheaval. Such, however, is the only explanation offered of the 

 flexures of the Tertiary strata at the base of the Alps, no account 

 being considered necessary of the supernatural force demanded for 



* Bull. Soc. G-eol. France, 2^ serie, vol. ii. 1853, p. 41. I do not know if the 

 work of which this paper is but a prodrome, ever appeared. 



