GEOGRAPHICAL EVOLUTION. 595 



Of absolute chronology in such questions science can as yet give no 

 measure. How many millions of years each formation may have 

 required for its production, and how far back in time may be the era of 

 any given group of fossils, are problems to which no answer, other than 

 a mere guess, can be returned. But this is a matter of far less moment 

 than the relative chronology, which can usually be 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 move- 

 ment. The mere fact that they are of marine origin shows, of course, 

 that the land owes its origin to some kind of terrestrial 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 geological 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, accord- 

 ing 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, however, they manifest increasing signs 

 of commotion. Their undulations become more frequent and steeper, 

 until, entering 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. 



Yet even in the midst of such apparent chaos it is not impossible to 

 trace the fundamental law and order by which it is underlaid. The 

 prime fact to be noted is the universal plication and crumpling of rocks 

 which were at first nearly horizontal. From the gentle undulations of 

 the strata beneath the plains to their violent contortion and inversion 

 among the mountains, there is that insensible gradation which connects 



