352 GEIKIE 



accurately fixed for each country, and on which all attempts 

 to trace back the history of the land must be based. 



While, then, it is true that most of the materials of the 

 solid land have been laid down at successive periods under 

 the sea, and that the relative dates of their deposition can be 

 determined, it is no less certain that the formation of these 

 materials has not proceeded uninterruptedly, and that they 

 have not finally been raised into land by a single movement. 

 The mere fact that they are of marine origin shows, of 

 course, that the land owes its origin to some kind of terres- 

 trial disturbance. But when the sedimentary formations are 

 examined in detail, they present a most wonderful chronicle 

 of long-continued, oft-repeated, and exceedingly complex 

 movements of the crust of the globe. They show that the 

 history of every country has been long and eventful; that, 

 in short, hardly any portion of the land has reached its 

 present condition, save after a protracted series of geo- 

 logical revolutions. 



One of the most obvious and not the least striking features 

 in the architecture of the land is the frequency with which 

 the rocks, though originally horizontal, or approximately so, 

 have been tilted up at various angles, or even placed on end. 

 At first it might be supposed that these disturbed positions 

 have been assumed at random, according to the capricious 

 operations of subterranean forces. They seem to follow no 

 order, and to defy any attempt to reduce them to system. 

 Yet a closer scrutiny serves to establish a real connection 

 among them'. They are found, for the most part, to belong 

 to great, though fractured, curves, into which the crust of 

 the earth has been folded. In low countries far removed 

 from any great mountain range, the rocks often present 

 scarcely a trace of disturbance, or if they have been 

 affected, it is chiefly by having been thrown into gentle 

 undulations. As we approach the higher grounds, how- 

 ever, they manifest increasing signs of commotion. Their 

 undulations become more frequent and steeper, until, en- 

 tering within the mountain region, we find the rocks curved, 

 crumpled, fractured, inverted, tossed over each other into 

 yawning gulf and towering crest, like billows arrested at 

 the height of a furious storm. 



