164 THE STORY OP THE EARTH AND MAN. 



areas became or remained submerged. Another 

 American geologist has largely illustrated the fact 

 that the movements which threw up the Appalachian 

 folds were strongest to the eastward, and that the 

 ridges of rock are steepest on their west sides, the 

 force which caused them acting from the direction of 

 the sea. It seems as if the Atlantic area had wanted 

 elbow-room, and had crushed up the edges of the 

 continents next to it. In other words, in the lapse of 

 the Palaeozoic ages the nucleus of the earth had shrunk 

 away from its coating of rocky layers, which again 

 collapsed into great wrinkles. 



Such a process may seem difficult of comprehension. 

 To understand it we must bear in mind some of its 

 conditions. First, the amount of this wrinkling was 

 extremely small relatively to the mass of the earth. 

 In the diagram on page 162 it is greatly exag- 

 gerated, yet is seen to be quite insignificant, however 

 gigantic in comparison with microscopic weaklings 

 like ourselves. Secondly, it was probably extremely 

 slow. Beds of solid rock cannot be suddenly bent into 

 great folds without breaking, and the abruptness of 

 some of the folds may be seen from our figure, copied 

 from Rogers (page 162), of some of the foldings of the 

 Appalachian Mountains. Thirdly, the older rocks 

 below the Carboniferous and the Devonian must have 

 been in a softened and plastic state, and so capable of 

 filling up the vacancies left by the bending of the hard 

 crust above. In evidence of this, we have in the Lower 

 Permian immense volcanic ejections — lavas and other 



