INTRODUCTION, 2/ 



showing how individual strata might remain horizontal, while 

 others might be tilted or even be thrown into a quite perpen- 

 dicular position, others again might be bent into the form of 

 arches. The occurrence of crust-inthrows, together with the 

 effects of surface denudation, might give shape to mountains 

 and valleys, plateaux, and low- lying plains. Mountains, hej 

 said, might also originate from upward action of the volcanic , 

 forces in the crust. In cases of active volcanic eruption, ashy ; 

 and fragmental rock materials were ejected, intermixed with 

 sulphurous vapours and mineral pitch. 



Thus Steno's work already, contained the kernel of much 

 that has been under constant discussion during the two cen- 

 turies which have passed since his death; and if one reads 

 trie most recent text-books of geology, it will be evident that 

 science has not yet securely ascertained the share that is to 

 be assigned to subsidence, to upheaval, to erosion, and to 

 volcanic action in the history of the earth's surface conforma- 

 tion in different regions. 



Descartes (1596-1650), in his Principia Philosophies, founded 

 a cosmology upon his famous principle of the constancy of the 

 amount of motion or "momentum" in the universe. The 

 earth, he states, like all other bodies of the universe, is com- 

 posed of primitive particles of matter in which a whirling 

 motion is inherent, and they have aggregated themselves into 

 the form of a sphere. During the gradual cooling of the earth 

 the outer layers consolidated as a firm crust, while the nucleus 

 still continued incandescent. The coarser and heavier primi- 

 tive particles of the earth, as they rotated, collected round the 

 centre, while the finer and lighter particles gathered in the 

 outer regions and formed the crust, composed of metallic, 

 saline, and aqueous parts. Crust-rupture has from time to 

 time given origin to continents, seas, mountains, and valleys; . 

 according to Descartes, volcanic phenomena and fissure in- 

 jections are results of the high temperature of the earth's ! 

 interior. 



G. F. Leibnitz (1646-1716), the mathematician and physicist, 

 accepts in his Protogaa the Cartesian view, that primitive 

 matter had a fluid consistency owing to the tremendous initial 

 heat, and that the earth's spherical form was derived from the 

 aggregation of whirling ultimate elements or " monads " of 

 matter. In place of the Cartesian principle of momentum, 

 Leibnitz starts from a dynamical basis, and assumes a force 



