J. D. Dana on American Geological History. 329 



this, from the melting snows of the declining glacier epoch. 

 The frequent absence of fine stratification, so common in the 

 material of this upper terrace, has often been attributed to a 

 glacier origin. 



According to this view, the events of the Post-tertiary Period 

 in this country make a single consecutive series, dependent 

 mainly on polar or high -latitude oscillations : — an elevation for 

 the first or Glacial Epoch ; a depression for the second or Lauren- 

 tian Epoch : a moderate elevation again, to the present height, 

 for the third or Terrace Epoch. 



The same system may, I believe, be detected in Europe ; but, 

 like all the geology of that continent, it is complicated by many 

 conflicting results and local exceptions ; while North America, 

 as I have said, is like a single unfolding flower in its system of 

 evolutions. 



There is the grandeur of nature in the simplicity to which 

 we thus reduce the historical progress of this continent. The 

 prolonged oscillations of the crust, caused by pressure from the 

 southeast beneath the Atlantic, which reach on through the Pa- 

 laeozoic ages, producing the many changes of level in the Silurian 

 and Devonian, still others of greater frequency in the Carbonif- 

 erous, and then, as in an outburst of long emprisoned energy, 

 throwing up the range of the Appalachians, with vast effusions 

 of heat through the racked and tortured crust, next go on de- 

 clining as the Jurassic and Cretaceous Periods pass, and finally 

 fade out in the Tertiary. The northern oscillations, perhaps be- 

 fore in progress, then begin to exhibit their effects over the high 

 temperate latitudes, and continue to the Human Era. The sink- 

 ing of Greenland, now going on, may be another turn in the 

 movement ; and it is a significant fact, that, while we have both 

 there and in Sweden northern changes of level in progress, such 

 great secular movements have nowhere been detected on the 

 tropical parts of the continents. 



In deducing these conclusions, I have only stated in order the 

 facts as developed by our geologists. Were there time for a 

 more minute survey of details, the results would stand forth in 

 bolder characters. 



The sublimity of these continental movements is greatly en- 

 hanced when we extend our vision beyond this continent to 

 other parts of the world. It can be no fortunate coincidence, 

 that has produced the parallelism between the Appalachian 

 system and the grand feature lines of Britain, Norway, and 

 Brazil, or that has covered the north and south alike with drift 

 and fiords. But I will not wander, although the field of study 

 is a tempting one. 



In thus tracing out the fact, that there has been a plan or sys- 

 tem of development in the history of this planet, do we separate 



SECOND SERIES, VOL. XXII, NO. 66. — NOV., 1836. 



42 



